About 500 District of Columbia government employes representing a coalition of 14 city labor unions staged a rally on the steps of the District Building yestgerday afternoon to protest Mayor Marion Barry's refusal to begin collective bargaining on this year's wage increase.

Carrying signs declaring "Barry Is a Bummer" and "Collective Bargaining, Not Unilateral Decisions," and chanting "Don't Dictate, Negotiate," city teachers, police officers, firefighters, sanitation workers, transportation department employes, jail guards and a host of others gathered at the spirited rally to hear union leaders call for city-union negotiations for a 9.1 percent pay raise comparable to that recently given federal government workers.

"Mayor Barry," said Joslyn Williams, head of the political arm of the Greater Washington Center Labor Council, "You are not beyond the laws of the District of Columbia. The laws say you must negotiate and by God, you are going to negotiate."

Meanwhile, far away from the demonstration, in the studios of WDVM-TV, Barry, who has said he would not "negotiate in the streets," said in a live interview that he did not believe the city's work force supports the unions' leadership. The mayor urged the union leaders to begin bargaining for 1982, but said he expected the dispute to wind up in court.

George Johnson, head of the sanitation workers union, had this reply: "Well, he can take it to court; we're taking it to the streets."

Yesterday's demonstration came after Barry's statement Monday that despite an Oct. 10 ruling by the city's Public Employee Relations Board (PERB), he would not bargain collectively with the 14 city unions over this year's pay increase.

The board had granted a petition by the unions to certify them all together, for this year only, as a "unit" for bargaining purposes that would meet the requirements fo the city's new merit personnel act.

On Monday, however, Barry distributed an opinion by Corporation Counsel Judith Rogers, the city's chief legal officer, saying that the decision by PERB was "contrary to law and exceeded the PERB's statutory authority."

Barry said he would go ahead with a 5 percent cost-of-living raise for the city's 31,000 employes, retroactive to Oct. 1, adding that the 9.1 percent increase demanded by the protesters would requre laying off 3,400 workers or raising $29 million through new taxes.

Following the demonstration, union leaders urged the workers to wait inside the District Building for the mayor to return so that bargaining could begin. When they found the doors locked and guarded by building security guards, International Brotherhood of Police Officers union president Larry Simons vowed: "We'll be back tomorrow."