WHEN THE METS take the field in their new ballpark in 2009, Jackie Robinson will be the angel looking over their shoulders. Ballplayers in hardhats and elected officials gathered in Queens yesterday for a groundbreaking ceremony for the new old-style ballpark. For an estimated $20 million a year, banking giant Citigroup got a 20-year deal that will put its name on Citi Field, the 45,000-capacity ballpark now being built just east of the 42-year-old Shea Stadium. But the main entrance, modeled on the one in Brooklyn's old Ebbets Field, will be called the Jackie Robinson Rotunda, it was announced at yesterday's gathering. The vast space will include a statue of Robinson and tell his story "not only as a great baseball player, but as one of the great Americans," Mets owner Fred Wilpon said. Robinson broke the color barrier in Major League Baseball when he took the field with the Brooklyn Dodgers at Ebbets Field in 1947. He followed his Hall of Fame career with leadership in business and civil rights. Wilpon said that the Mets and Citigroup would work with the the Jackie Robinson Foundation to create a Jackie Robinson Museum and Learning Center in lower Manhattan, as well as fund scholarships for "young people who live by and embody Jackie's ideals." "It is my hope that, as individuals and groups walk through the rotunda, that they will begin to be inspired and to begin to think about their own lives and what the meaning of their own lives is," said Robinson's widow, Rachel Robinson. "For kids who never got a chance to see Jackie play . . ., it's going to be a great education on the man himself and a fitting tribute to one of the great human beings," said Mets manager Willie Randolph, who was joined by David Wright, Jose Reyes and other players. Shea Stadium namesake William Shea, the New York power lawyer who helped give birth to the Mets in 1962, will be honored elsewhere in the park. Asked whether the Mets had considered naming the new stadium after Robinson, Wilpon replied: "We certainly thought about that. But with the economics that go along with building a stadium like this, it is imperative that we receive revenues." Mayor Bloomberg said those who think the Flushing ballpark should be named after Robinson and not sold for naming rights "aren't the ones putting up the money." He added, "The Wilpons obviously need the money. If you're going to have private people pay for stadiums, then they've got to find a ways to pay for it." Citigroup Vice Chairman Lewis Kaden said the bank, which employs 25,000 people in the city, "has just won the World Series of sports sponsorships." The construction timetable, which will put the Mets in their new home on Opening Day in 2009, has already meant the loss of hundreds of parking spaces. "During the construction, there is going to be a little bit of pain," Bloomberg conceded. He added: "When you get done, you're going to have a brand-new stadium . . . This is a wonderful thing for this part of Queens." Citi Field's design - 12,500 fewer seats than Shea, but seating closer to the diamond - will cut the amount of foul territory third baseman Wright has to guard. With a sly smile, Wright told the Daily News, "It's a beautiful thing, a beautiful thing - less room for me to cover at third base and more balls [will] get out of play for foul balls - and that's a good thing, no matter how you slice it, for a hitter." The Mets are putting up more than $600 million for the new stadium, which the city and state are also supporting with a total of $165 million for such costs as infrastructure and site preparation. Graphic SHEA STADIUM Opening Day: April 17, 1964 Dimensions (in feet): Left Field: 338 / Left Center: 371 / Center: 410 / Right Center: 371 / Right Field: 338. Seating capacity: 57,333 Features: 45 luxury suites on one level / four public elevators / Fan Fest family entertainment area beyond right-field bullpen / picnic area beyond left-field bleachers / Mets Hall of Famer busts near The Diamond Club Restaurants: The Diamond Club, The Grill Room CITI FIELD Opening Day: April 2009 Dimensions (in feet): Left Field: 335 / Left Center: 379 / Center: 408 / Right Center: 391 / Right Field: 330 Seating capacity: About 45,000 Features: Jackie Robinson Rotunda, with statue of the baseball great / 57 luxury suites on three levels / 12 public elevators / expanded Fan Fest on concourse level / enhanced picnic area / interactive Mets museum with club memorabilia and Hall of Fame displays Restaurants: Ebbets Lounge, Sterling Lounge, Left Field Club Restaurant and Promenade Grill