The 1984 Summer Olympics are still three years off, but the U.S. Olympic Committee will begin gearing up for the Los Angeles Games with the opening Thursday of the six-day National Sports Festival in Syracuse, N.Y.

More than 2,600 athletes are scheduled to compete in 33 winter and summer Olympic sports at the festival, which is designed by the USOC as a way to promote interest in the Olympics and to provide the athletes with world class competition.

Formal opening ceremonies for the event, which is expected to attract many 1980 U.S. Olympic athletes who missed the Moscow Games last year because of the boycott protesting the Soviet invasion of Afganistan, are scheduled Thursday in the 52,000-seat Syracuse Carrier Dome.

In finest Olympic tradition, the athletes and coaches will parade into the Dome for the lighting of the National Sports Festival flame, from a torch carried to Syracuse from the summit of 14,000-foot Pikes Peak in Colorado.

The festival is not strictly a part of the Olympic selection process for 1984, although it is expected to attract most athletes who will be leading contenders for slots on the 1984 U.S. Olympic teams. The Olympic selection will take place at Olympic Trials or other national events as the Games approach.

"Thee are big names and there are names you have not heard, but by 1984, you will know many of them," said Col. F. Don Miller, executive director of the USOC. "The National Sports Festival serves to showcase the great wealth of amateur sports talent in the United States."

The brainchild of former USOC president Robert J. Kane, who argued that American athletes should have an opportunity to test their mettle in Olympic-style surroundings in non-Olympic years, the festival was held at the USOC training facility in Colorado Springs in 1978 and 1979, the first two years of its existence.

It was not held last year, an Olympic year, and was moved to Syracuse this year. Among the better-known athletes slated to compete are Georgetown University-bound basketball players Pat Ewing, Anthony Jones Thompson will coach the Eastern Regional team at the festival, which will draw seven of Parade Magazine's top 10 all-Americans and 14 of McDonald's all-American team of 25.

UDC's Earl Jones will also play on the Eastern team, as will Johnny Dawkins, 17, a standout point guard from Mackin High School in Washington, the only high school underclassman among the 48 basketball players competing at the festival.

It was at the 1979 National Sports Festival that the nucleus of the U.S. Olympic Hockey team that defeated the Russians in the 1980 Winter Games at Lake Placid was formed, and a strong hockey showing is expected in Syracuse.

Bobby Carpenter, the high school hockey standout who was drafted by the Washington Capitals, will be there, as will Marc Behrend, the sophomore goalie who anchored Wisconsin's national championship team last winter.

Edwin Moses, the 1976, Olympic champion and world record holder in the 400-meter intermediate hurdles, is one of about 20 track and field athletes expected to return from European competitions for the Festival.

Others include Al Oerter, four-time Olympic champion int he discus; Willie Banks, the U.S. record holder in the triple jump; Larry Myrics, the 1979 World Cup champion in the long jump; Evelyn Ashford, the 1979 World Cup winner in the 100 and 200 meters and the U.S. record holder in both events, and Pam Spencer, the U.S. record holder in the high jump.