The Super Bowl champion Washington Redskins, accustomed this season to playing and winning in the rain, will likely have to make their triumphant parade through Washington today in the same foul stuff.

The National Weather Service forecast calls for rain, heavy at times, throughout the day, with temperatures predicted to be in the mid-40s at noon, when the parade is scheduled to begin with a ceremony on Pennsylvania Avenue NW in front of the District Building.

President Reagan, who greeted the returning NFL champions Monday at Dulles Airport, decided yesterday afternoon to give all federal government employes two hours off--between noon and 2 p.m.--to watch the parade. D.C. Mayor Marion Barry is also giving city employes two hours off. The administrative leave will not be charged as vacation.

Washington area schools, with the exception of those in Alexandria, are permitting students who bring notes from their parents to take the day off to attend the parade.

After the noon ceremony in front of the District Building, during which Redskins players, coaches, owners and city officials are expected to speak, the parade will move south on 14th Street, then east on Constitution Avenue. It will disband at Third and Constitution NW, District police said yesterday.

"We are anticipating a large crowd, but we are not going to permit the kind of conduct public drinking and destruction of property that occurred on Sunday night," Deputy Police Chief John Connor of the special operations division said yesterday. During the frenzied post-Super Bowl celebration, 26 people were arrested, 40 others were injured, six store windows were broken and five police cars were damaged. "We are not going to put up with that kind of behavior and we don't anticipate it," Connor said.

Redskins players, who will bring up the rear of a parade led by at least six local high school marching bands, along with assorted politicians, Redskinettes, and a truckload of hogs, are expected to ride in open convertibles.

One group that will be conspicuous by its absence from the parade is the Redskins marching band. Band members, who received neither a free seat aboard Jack Kent Cooke's chartered DC10 to Pasadena nor a free ticket to the Super Bowl once they paid their own way out, are "disgusted at the way we've been treated," according to Stuart Eisen of the brass section.

Eisen said the 40 band members who paid their way to get into the Super Bowl were ordered by stadium security officials not to play "Hail to the Redskins" during the game.

A security man "says he's with the Rose Bowl but the orders come from the NFL. And he says we can't play, and if we do he's gonna throw us out of the stadium," Eisen said. "After that and Cooke and everything, I don't even know if there's going to be a band next year. We're not being treated like an orphan. We're treated like the stepchild of an orphan."

After the parade, expected to end by 2 p.m., Redskins players and coaches will attend a private reception given by D.C. Del. Walter E. Fauntroy at the Hyatt Regency Hotel, 400 New Jersey Ave. NW.

At the reception, to which all members of Congress have been invited, dolphin will be served, along with pigs in a blanket and Danish lobster tails. Jeff Wind, chef at the Hyatt, which is picking the $18,000 tab for the party, has carved two tons of ice sculpture for the event. One of the sculptures is a Redskins hog.