LEAD: ''In many ways we keep winning,'' the Rev. Jesse Jackson said Tuesday after losing the Pennsylvania primary by a wide margin. ''We keep getting popular votes. We keep getting delegate votes. We keep setting the agenda for the campaign.''
''In many ways we keep winning,'' the Rev. Jesse Jackson said Tuesday after losing the Pennsylvania primary by a wide margin. ''We keep getting popular votes. We keep getting delegate votes. We keep setting the agenda for the campaign.''
That isn't all. In the view of politicians and people who follow politics, he has already won something vastly more important: he has won a solid place in history.
Whether or not he is elected President, whether or not he is even nominated for Vice President, whether or not he wins more primaries, the world is likely to remember 1988 as the Year of Jackson - the year when, for the first time in American history, a black made a serious bid for the White House and was taken seriously by the electorate. 'The Highest Compliment'
''Americans have opened their minds to him and his candidacy,'' said former Vice President Walter F. Mondale in a recent interview. ''They took him seriously. That's the highest compliment. They have thought hard about voting for him, and millions upon millions have done so.''
Mr. Mondale added: ''Jesse Jackson is now a significant power in national politics. No black man has been that before.''
A prominent Democrat of a younger generation, Senator Christopher J. Dodd of Connecticut, said he was ''totally convinced'' that Mr. Jackson recognized that his candidacy was ''the seminal event of the year'' and that the Chicago clergyman would therefore do his utmost to advance the cause of the Democratic ticket in November, whether he is one of the nominees or not.
''Jesse Jackson is too smart to get himself into the position of being blamed if we don't prevail this fall,'' Mr. Dodd said. ''He's not going to create havoc, either at the convention or after it, and he's not going to make a lot of demands or issue any ultimatums. How in the world could it help the black community or Jesse Jackson to have him break with the Democrats?''
Senator Dodd and others expect Mr. Jackson to concentrate on issues, and he himself said this week that, while he battles for more delegates and perhaps even an upset victory in the California primary on June 7, the remainder of the campaign would be about ''the future direction of the party.''
But he can argue issues without risking a split in the party, said Senator George J. Mitchell of Maine, because there is a big difference ''between pushing his agenda and abandoning the enormous discipline and restraint he has shown so far.''
One reason why Mr. Jackson's mark on history is so clear is that it shows something political experts plainly did not expect: that to an increasing number of Americans, color just does not matter. 'What Matters Is Jobs'
Several weeks ago, in the days before the Wisconsin primary, Mr. Jackson drew huge crowds of ethnic voters in Milwaukee, including many Polish-Americans and Serbian-Americans and German-Americans who told a reporter that in past Presidential primaries they had supported George C. Wallace, the supreme adversary of Mr. Jackson and his colleagues in the civil rights movement of the 1960's. Mr. Jackson's appeal, to some degree at least, clearly reaches well beyond his core of blacks, liberals and students.
''Doesn't matter to me whether the guy's colored or not,'' one of the voters said, as matter-of-factly as he might have said it did not matter whether the candidate was tall or short. ''What matters is whether the guy can save jobs.''
Wisconsin was special, but not unique. Reporters have found those same reactions in Greenfield, Iowa, the small town where he made his headquarters in that state for the caucuses, and in Brooklyn, Kalamazoo, Mich., and McKeesport, Pa.
Prof. James David Barber of Duke University, who has written several books on the Presidency, credits Mr. Jackson with having done for blacks what Alfred E. Smith and John F. Kennedy did for Roman Catholics. Mr. Jackson has ''registered a social and cultural shift,'' Mr. Barber said, ''that enables us all to entertain the possibility of having a black President in this country.''
Similar shifts were spoken of after Geraldine A. Ferraro was chosen as the Democratic nominee for Vice President in 1984; it remains to be seen whether her candidacy has hastened the day a woman will run for and win the Presidency. At first, her nomination seemed to energize the Democrats, and then questions over her finances bogged them down. In the end, a New York Times/CBS News Poll of voters indicated she added about half a percentage point to the Democratic ticket's strength.
The change in America that Mr. Jackson's success reflects does not, of course, suggest that racism is dead in the United States or that Mr. Jackson or another black candidate would not face an uphill fight for the Presidency.
Even so, in Mr. Mondale's view, Mr. Jackson's success has ''made Americans feel pretty good about their country and about themselves, good that this sort of thing could happen in our nation first.'' Chisholm Candidacy in 1972
Mr. Jackson is not the first black candidate for President. Former Representative Shirley Chisholm of Brooklyn ran in 1972, trying for a share of the black vote and for what few women's rights votes were then available. She got 151.95 delegate votes at the Democratic National Convention that year. And Mr. Jackson, of course, ran in 1984, in what was then regarded as a protest candidacy. He won the Louisiana and District of Columbia primaries and received 465.5 votes at the convention.
To some degree the Chicago civil rights leader has benefited this year from a fragmented field with no other nationally known candidates. And to some degree he has profited from slowly changing public attitudes. But Mr. Jackson has also done much to help himself, moderating his tone if not his positions and making clear his desire to be considered part of the Democratic mainstream.
''He has shown himself to be the most powerful communicator in either party,'' Mr. Mondale said. ''His greatest asset is his skill as a speaker. This is the cleverest, most touching, most engaging orator we have in America -a man who can take an issue and make it sing as if it had legs.''
But that very quality troubles many people, who think it obscures failures as an administrator and as a practical political operative.
''He has a terrible track record in running his civil rights organizations, and he has no experience whatever in elective office,'' said Mr. Barber, the Duke professor. ''There is no reason at all to think that he could stay afloat in the strange world of insiders' Washington. 'Administrative Shortcomings'
''Somehow, people think it would be racist to examine his record closely and hold him to a high standard,'' the professor continued. ''That's why we haven't heard nearly enough about his administrative shortcomings and his lack of any experience at all in elective office. Exactly the opposite is true, of course. It's racist and patronizing to let him slip through just because he's black.''
Be that as it may - and although they will not say so for the record, many leading Democrats agree with Mr. Barber - few who have known Mr. Jackson well question his intelligence. Senator Terry Sanford, a North Carolina Democrat who has known Mr. Jackson since his days as a student demonstrator, has often described him as having the shrewdest political mind in America.
He will need a lot of political judgment in the months to come, and as it becomes clearer that Gov. Michael S. Dukakis of Massachusetts, not Mr. Jackson, will be the nominee, Mr. Jackson's supporters may press him to be more aggressive, to demand rather than discuss. Backbiting over Pennsylvania scheduling was developing as the disheartening returns came in Tuesday night. As hope of a Jackson nomination dims, rivalries and individual ambitions within the Jackson campaign may take a front seat. Jackson Support Called Vital
Ted Van Dyk, a Washington consultant who has been involved in many Presidential campaigns in the last quarter of a century, thinks Mr. Jackson, armed with what Mr. Van Dyk calls ''the incredible faith of blacks and other disadvantaged groups,'' already has ''the power to keep Dukakis from becoming President and the power to keep Dukakis from governing if he does win.''
''The fact is,'' Mr. Van Dyk said, ''without Jesse's support within the party no white Democrat can accomplish much on a national scale.''
Like Mr. Van Dyk and almost all leading Democrats, Robert S. Strauss, the former Democratic national chairman, expects Mr. Dukakis to be the party's Presidential nominee. But Mr. Strauss hails Mr. Jackson's ''astonishing success'' and says: ''The question is not, 'How do we handle the Jackson problem?' The question is, 'How do we use Jackson's enormously increased stature to help the party and also to advance his agenda?' ''
Mr. Strauss is urging that after some preliminary explorations, Mr. Dukakis and Mr. Jackson sit down and discuss how to assemble the best ticket, which Mr. Strauss, who is from Texas, believes should be composed of Mr. Dukakis and a Southern running mate, and Mr. Jackson's role in the campaign.
''Jackson can be a power broker in the best sense, not the worst,'' Mr. Strauss said. ''He needs to be seen putting together something that helps the party win, helps produce results on the issues he has been talking about, rather than doing something for himself. If he can do that he becomes a premier political figure, with all kinds of possibilities ahead of him. If not, he could dissipate much of the credibility he has built up this year, which would be a real tragedy.''