You never would have known it by the way he behaved during his 22 years on Capitol Hill, but former Virginia Rep. Joel Broyhill thinks the District of Columbia is a great city and feels that he is a part of it. At least that's what Broyhill told nearly 400 persons last week at the Metropolitan Washington Board of Trade's "Man of the Years" dinner at the Shoreham Americana Hotel.

Broyhill was not the "Man of the years." That honor went to Joseph H. Riley, president of National Savings and Trust Co. But Broyhill, the roaster, still calling himself a politician, was the star of the show. "I feel sort of like a mosquito at a nudist colony," Broyhill said. "I know what I'm here for but I don't know where to begin."

Ten minutes of the Broyhill wit - playing on Irish Catholics, old age and sex and Joe Riley - was displayed in good form. Then, rhetorically including himself among the populace whose self-government he at one time adamantly opposed, Broyhill declared, "We are a great town."

Mayor Walter Washington helped lead the applause when Broyhill said the city was great even though it didn't receive enough money from Congress. "If Joel Broyhill keeps speaking like that," City Council Chairman Sterling Tucker added later, "We're going to send him back to the Congress."

The mayor sounded a lot like a candidate, even though he still says he's uncertain about running for re-election in 1978. He talked about the greatness of the city, the greatness of Joe Riley and the greatness of the Board of Trade.

The mayor asked all those in favor of building the proposed $110 million convention center at Mt. Vernon Square to stand. Many did, including parking lot baron Dominic F. Antonelli Jr., who owns more than $1 million worth of land around the center site. Antonelli popped to his feet and stretched out his arms, motioning enthusiastically for others to join him.

Tucker, another mayoral hopeful, only got three minutes on the program and some polite applause. Council member Marion Barry, who also wants to be mayor, could muster only a seat in the audience at the table of Linowes & Blocher, the influential real estate law firm.

The mayor told the audience the evening was reminiscent of the time he was being honored by a college and a dog strayed across the stage during the ceremony. His university hosts were embarrassed, but Washingtonwas not. "I told him, 'Mr. President I want you to know the mayors find friends anywhere they can. That dog is welcome, and that's not a stage joke.'"

Riley, the "Man of the Years," finally got his chance, after several speeches and the presentation of a trophy to the chef. "I don't mind sharing this night with that chef," Riley told his hosts. "He not only cooks better than most of you. He speaks better than most of you, too."