INDIANA DEFEATS NORTH CAROLINA, 63-50, FOR N.C.A.A. TITLE

PHILADELPHIA, March 30— The Indiana basketball team is getting to feel at home in the City of Brotherly Love. For the second time in five years, Indiana won the National Collegiate Athletic Association championship in the Spectrum here. The Hoosiers, sparked by Isiah Thomas, a sophomore all-America point guard, pulled away in the second half and went on to a 63-50 triumph over North Carolina tonight in the final of the 43d annual tournament. Thomas finished as the game's high scorer with 23 points, and led a 12-4 spurt at the beginning of the second half that broke open a close game.

Bobby Knight, Indiana's coach, said, ''My first thought would be, when will the N.C.A.A. Basketball Tournament Committee come back to Philadelphia?''

The first time the final was played in Philadelphia was 1976, and an undefeated Indiana team beat Michigan, 86-68. Returning to the Spectrum before 18,276 spectators tonight, Indiana won again, but did so with a team that finished with a 23-9 record for the season. This is the most losses by an N.C.A.A. champion; the previous high was Marquette's seven in 1977.

For North Carolina, it was another case of frustration in the title game. Dean Smith has taken North Carolina to the final three times in his 19 seasons there, and each time Carolina has lost - to U.C.L.A. in 1968, to Marquette in 1977 and now to Indiana.

Asked how he felt about getting so near but not winning, Smith said, ''We can be like Penn State football, No. 2 all the time.'' North Carolina did, however, win the national title in 1957 under Coach Frank McGuire. The Hoosiers have won four N.C.A.A. basketball championships under two coaches. Branch McCraken guided them to the championship in 1940 and 1953.

Shortly before the game was to be played, the N.C.A.A. Basketball Committee met to decide whether to proceed in view of the assassination attempt on President Reagan earlier in the day. Following word that the President had left the operating room and was beginning recovery, the nine-man committee voted unanimously to go ahead with the game. Because of this meeting, the game's start was delayed seven minutes, from 8:23 P.M. until 8:30. NBC Sports also went ahead with plans to televise the game nationally.

Indiana finished strongly, leading by 14 points with two and a half minutes to play. This ended an impressive tournament for the Big Ten Conference champions. En route to the final, they beat Maryland by 35 points, Alabama-Birmingham by 15 and St. Joseph's by 32.

But back in December it did not appear that Indiana would get this far. That's when the Hoosiers lost five of their first 12 games, including a 65-56 loss to the Tar Heels at Chapel Hill, N.C., on Dec. 20. Knight Praises Maturity

Tonight, Indiana was a different team in skills and defensive talents, a team that Knight said ''has matured more than any I have seen.''

Thomas, who has led the team in scoring all season, made only one of seven field-goal attempts in the first half. Indiana led, 27-26, at intermission, but only because Randy Wittman hit a jumper from the left corner at the buzzer. After the intermission, however, Thomas started quickly, making two spectacular steals that he converted into baskets.

''Isiah Thomas's steals were the turning point,'' said Smith. Thomas said: ''In the second half we were a lot more patient. I shot a little better.'' He shot more than just a little better. He not only scored on the steals but added two quick baskets on fine lead passes by Jim Thomas, the other Indiana guard. Two Thomases Excel

Jim Thomas, who went into the semifinal game against Louisiana State Saturday early when Isiah got into foul trouble, came in early again tonight. This time he replaced a forward, Ted Kitchel, who had three personal fouls in the first four minutes. Jim Thomas, no relation to Isiah, is also a sophomore. He lives in Fort Lauderdale, Fla. Isiah lives in Westchester, Ill.

For their play both Saturday and tonight, Isiah and Jim Thomas were named to the all-tournament team, along with Jeff Lamp of Virginia, Al Wood of North Carolina and Landon Turner of Indiana. Isiah Thomas was named the tournament's outstanding player.

Earlier tonight, Lamp scored 25 points to lead Virginia to a 78-74 victory over L.S.U. in the consolation game for third place. Jim Thomas was superb on defense, that part of the game on which Indiana and Knight pride themselves. The Hoosiers play a man-to-man defense that harries the opponent with a sticky persistence. Jim Thomas had the unenviable job of entering the game and guarding Kitchel's man, Wood. Good Job on Wood

Wood, 6-6, a senior all-America forward, had scored 39 points in the victory over Virginia, a record for a semifinal game. He was held to 18 points tonight, 4 below what he had been averaging in this tournament, and it was mainly because of Jim Thomas's defense. And Thomas did this even though he is three inches shorter than Wood.

The other Hoosiers were at their defensive best. North Carolina's 50 points was the lowest losing score in an N.C.A.A. championship game since Kentucky beat Oklahoma State for the title, 46-36, in 1949. Indiana's winning score was the second lowest for a champion in the final in the last 18 years.

Indiana, despite losing the 6-8 Kitchel early in the game, took down 33 rebounds to only 27 for North Carolina. The rebounding was even in the first half, so the Hoosiers' edge on the boards, along with Isiah Thomas's play, helped them break it open in the second half. But this has been the pattern for Indiana, which trailed L.S.U. by 3 points at intermission in the semifinal only to leave the Tigers behind with a 9-point spurt at the start of the second half.

Another factor that hurt North Carolina was the loss of James Worthy. He had to sit down with five minutes left in the game because he drew his fifth personal foul. This ended any chance for a comeback by the Tar Heels, who depend so much upon their big front line of Worthy, Wood and Sam Perkins, the freshman center.

Indiana's second-half drives to victory are the result of a belief in what the Hoosiers are doing. They might not be hitting the shots in the first half. But Knight's basic basketball of hard defense and patient offense eventually pays off. Pressure and Patience

''Ours is a game of doing what we want to do the whole game,'' Knight said. ''If we can do that, our ultimate objective is to break down a team over the whole 40 minutes. If we can stay with our defense and pressure the ball and stay with our offense and be patient, we're going into the last part of the game and we've got control.''

This was the blueprint that the players followed in this Final Four. It worked to perfection and to the national title. Indiana hit only 37.9 percent of its floor shots in the first 20 minutes and was down by 8 points midway through the first half. But the Hoosiers worked patiently back. North Carolina scored only 10 points in the last 10 minutes of the first half against the sticky Indiana defense after leading, 16-8. After the Hoosiers took the lead at the half on Wittman's shot, they never trailed.

Illustrations: Photo of N.C. vs. Indiana (Page B21) Photo of N.C. vs. Indiana