"Champions of American Sport," an exhibit of sports art that opens Tuesday at the National Portrait Gallery, honors through photographs, painting, sculpture and memorabilia the impact of sports heroes on the American imagination.

Supported by grants from Philip Morris Inc. and the Miller Brewing Co., companies that have been long involved in sponsoring sports, it is the first major exhibit devoted to outstanding American sports personalities. More than 500 items, on loan from various halls of fame and the families of athletes, celebrate the accomplishments of 100 American champions.

Marc Pachter, the museum historian who directed the three-year project, says the exhibit encourages a renewal of awe for the champions that have been entwined in American culture from the mid-19th century through the present.

"We still wonder about what makes a great champion," Pachter said. "Fundamentally, that's a mystery: what makes Joe DiMaggio's swing so majestic? Why are we so happy when we watch Willie Mays? The show just celebrates whatever that mystery is.

"Babe Ruth is really the supreme example of a man of intrigue. People are stunned by both his power and authority, as well as his needs. Ruth's capacities were unbelievable," Pachter said.

One of the Ruth items, a 1927 photograph of the Yankee-capped, pudgy-faced Ruth sitting with his bat, has been reproduced as the exhibit poster.

The show will remain in Washington through Sept. 7 before traveling to Chicago, Los Angeles and New York.

More than half of the 100 chosen athletes still are living. They will be honored by President Ronald Reagan, who has always been responsive to sports, at a White House reception Monday afternoon. Basketball's Bob Cousy, Willis Reed, Oscar Robertson, bill Russell, George Mikan and Red Auerbach; Olympic skating starts Tenley Albright and Dick Button; football's George (Papa Bear) Halas; jockey Eddie Arcaro, and track great Wilma Rudolph will be present.

Joining them will be the widows and families of athletes Jesse Owens, Joe Louis, Jackie Robinson, Vince Lombardi, Rocky Marciano, Wilbur Shaw, Ralph DePalma and Duke Kahanamoku.

"It's really a show about these 100 individuals," Pachter said. "So many Americans live by sports heroes. The show combines the world of art and the world of sports: we're showing the museum community the power of these athletes' own qualities. And we're showing the sports world one of the ways that the champions have been commemorated -- in writing, songs and art."

"Champions of American Sport" will run in conjunction with a similarly titled sports film festival by the Kennedy Center's American Film Institute which opens July 1. The festival of more than 40 films will combine Hollywood features with documentary motion picture tributes.

The National Portrait Gallery will show continuously its own half-hour film, "Champions of American Sport," which further examines the mystique of these winners. Johnny Unitas, Billie Jean King, Arthur Ashe, Willie Shoemaker and Ted Williams, among others, are featured trying to answer the question the exhibit presents: what is the special something in a champion?

Selecting the 100 champions was as much a task as gathering the portraits. Pachter and museum curators Kenneth Yellis and Beverly Cox chose the 100 because they were winners in their sports as well as charismatic figures.

They wanted athletes whose presence would guarantee a crowd, who caught the eye of the sportswriters of the day, who might have been the subject of a song or a film.

Many of the athletes were known to average Americans, even those who didn't read the sports pages every day. All of them were celebrities in their time, and were known, for the most part, to succeeding generations.

Baseball, which alone has given Americans hundreds of nationally recognized personalities, provided the hardest task for the curators. Deciding who to omit was difficult. Baseball, consequently, takes up the most space in the exhibit. It is represented by 17 figures, including a manager (Casey Stengel) and a commissioner (Kenesaw Mountain Landis.