The D.C. City Council approved emergency legislation yesterday that will give the District of Columbia's 12,100 policemen, firefighters and teachers the same percentage pay increase in October that most of the city's other employees will get.

A president committee that considered pay raises for D.C. and U.S. employees has recommended a 7 per cent pay increase but President Carter has not officially set the amount of the increase.

The council voted to approve the increae as an emergency measure to allow the teachers, firemen and policemen to get the pay increase at the same time other city employees do.

An identical bill is before the Council that would extend the pay raise beyond the 90 days that the emergency legislation allows. That bill would be in effect for only one year and is a stop-gap measure to deal with policemen, firefighters and teachers until the council can consider permanent legislation later this year that would establish a merit personnel system for all city employees.

Although this is the second year in which the council has tied police and firemen's wage increases to that granted other general schedule employees, the broad support among affected union leaders yesterday represents a turnabout in the positions that firefighter and police union leaders took last year.

They negotiated then directly with the mayor. But they indicated that they had lost confidence that Mayor Walter E. Washington and his administration can deliver to the police and firefighter unions what they promise at the bargaining table, union officials said.

They said that the new legislation guarantees them a floor for wage increases that removes a portion of the negotiating process from the political arena.

The legislation also guarantees police and firefighters a timely increase that is not dependent on negotiations with the city, which in the past has persisted well beyond the Oct. 1 start of the new fiscal year.

Currently, the District's teachers cannot bargain collectively. The School Board, instead of the Washington Teachers Union, negotiates with the city for teachers pay raises, and for years teachers have complained that their increases were below those granted to other city employees.

Two years ago, during negotiations between the city and the firefighters and police unions, the mayor promised union officials an 8 per cent increase efective in January, 1975, and a 10 per cent increase the following year.

But the City Council did not approved the increases and rolled them back to 6 and 4 per cent, respectively.

This year, the unions began lobbying with the city council to pass legislation that would guarantee them the same increases that other employees get while at the same time the unions would continue to bargain directly with city officials.

While union leaders said they were "happy" with the council's decision yesterday, the city personnel director George Harrod, complained that the legislation served to tie his hands.

Harrod told the Council that its action came at a time when unions were demanding such other benefits as overtime pay, premium for Sunday duty and night-time differential. Harrod said that the council-guaranteed pay increase would cost about $10.5 million a year and that additional benefits could add an estimated $21 million.

"My credibility is at stake," Harrod said. "I don't represent the mayor, but the entire city, and I would have appreciated a lower point to begin negotiations. I would have started at 4 or 5 per cent and would have tried to save the city money."