President Reagan's weekly radio broadcast was canceled last night and "Mr. Reagan's Neighborhood" took its place.

Clad in cardigan and sneakers, the chief executive asked the audience, "Won't you be my neighbor? If you're good, royalty'll visit your neighborhood . . ." He then greeted a goldfish, and turned to the audience. "Can you say Dense Pack?"

Just about anything goes at the Hexagon's annual comedy revue. This year, along with the president (a k a Donald S. Williams), even chicken meister Frank Perdue was fair game.

The 28th annual revue, titled "Fair Game" and staged by the nonprofit, all-volunteer theatrical troupe Hexagon, is devoted to raising money for the Washington Humane Society. Last night, for a special "gala performance" at $100 a seat, the Trinity Theatre in Georgetown, where the show will run through March 26, was just about full with guests in formal dress.

Mrs. Foggybottom, a snooty, high-society character otherwise known as Joan Cushing, a local comedian, delivered her first monologue, martini in hand, from a bar stool in the corner of the stage. She started off talking to Secretary of Transportation Elizabeth Dole about Metro.

"I said to Elizabeth Dole, 'Elizabeth, daaaarling--why not make the Green Line for people in the Green Book? And she said 'No, that would never work because the Green Line goes right through Prince George's County. And you know those people would never be caught dead in P.G. County . . . Oh well, I'm off to inspect I-66, but first I have to find two people and a dummy, so I can ride in the fast lane . . .' "

The objects of the musical satire also included Rita Lavelle, ousted director of the Environmental Protection Agency's hazardous waste cleanup program, and Perdue, who came to see the Hexagoners perform a skit about him.

In "The Golden Moment," a group of dancers dressed up like chickens were auditioning to become part of the Perdue brood:

There is a golden moment/One shining golden moment/When life is beautiful and happy/That's what we live our lives for/That's what we chickens strive for . . ./A chicken has his dreams/His golden moment too/When the chicken's chosen by Perdue.

The show's periodic "Newsbreaks" were anchored by WDVM newsman Gordon Peterson, Bob Ryan, introduced as "that wonderful weatherman" from WRC-TV, and Hexagon's Martha Manning. One of their news updates went something like this:

"As a result of falling oil prices Saudi Arabia announced today that it was selling England."

During intermission, Peterson and Ryan talked with Hexagon director Ron Sarro, a WDVM-TV reporter.

"I've done two things since November--my work at Channel 9 and this," Sarro said.

Ryan, jovial on stage and off, was asked why he had agreed to participate. "We bought these things," he said, gesturing to both his and Peterson's tuxedos, "so we've got to wear them every chance we get."

After the three-hour show, the 350 guests gathered at Georgetown Park for a sit-down dinner. A happy Bianca Beary, president of the Washington Humane Society, praised the show and then got down to serious business.

"We have very good luck with cats," she explained about the Society. "It's the dogs that get the shaft."