The Washington party season starts back into full swing this week and no matter how high the temperature rises, Thursday's black-tie gala performance of "La Cage aux Folles" will bring out some of the city's glittery and powerful. They will be there for the performance and a fancy sit-down supper for an intimate 600 hosted by the Shubert Organization and "La Cage" producer Allan Carr at the Departmental Auditorium, with some 3,000 ostrich feathers used as centerpieces.

While the smash Broadway musical that is expected to run for several months at the National Theatre doesn't open officially until Sept. 18, there will be a number of benefit performances before then. There will be regular theatergoers in the balcony, but the orchestra seats will be filled with social, political, White House, Supreme Court and media celebrities.

Among the first-nighters expected are Defense Secretary Caspar Weinberger, Health and Human Services Secretary Margaret Heckler, Sens. Paula Hawkins, Mark Hatfield and Paul Laxalt, Supreme Court justices Sandra Day O'Connor, Byron White, Thurgood Marshall and Harry Blackmun, Redskins Mark Moseley and John Riggins, former White House aides Mike Deaver and Joe Canzeri, White House press spokesman Larry Speakes, newsmen Ted Koppel and Steve Bell, singer Karen Akers and comedian Mark Russell. At the after-theater supper, one can be certain that Riggins and O'Connor will not be assigned to the same table.