The Washington Teachers Union delayed plans for a strike today against city schools when leaders announced yesterday that they will not gather their members for a strike vote before next Tuesday.

Harold Fisher, assistant to union president William Simons, said forecasts of snow for today and last night caused the union to delay calling a strike authorization meeting.

"We're waiting only because we are dealing with the weather situation in terms of mobilizing our people," Fisher said. "If the weatherman had not forecast a couple of inches of snow for tomorrow and Friday, we would move to get our people together more quickly."

Three factors militate against a strike this week, according to school officials. They are the cold weather, the planned distribution of paychecks Friday and the holiday Monday commemorating George Washington's birthday.

Meanwhile, the Federal Mediation and Conciliation Service reported yesterday that progress has been made in negotiations between the board and the union. John Rogers, a spokesman for the group, said "both sides are bargaining very seriously.

"There has been movement on both sides," Rogers added. "They came in with a good attitude. It has been a positive bargaining session."

Negotiations broke off by mutual agreement at 2:30 a.m. today and are scheduled to resume at noon.

Earlier last night, federal mediator John Wagner, assisting in the talks at Payne Elementary School, reported that both sides had agreed to continue talks beyond the midnight deadline for expiration of the most recent contract extension.

"I am very confident that things are moving well," Wagner said during a brief break in the talks. The two sides were still meeting at 2 o'clock this morning.

The deadline was set last month when federal mediators were asked to join the talks as a condition for a 30-day extension of the union contract with the board.The contract, which originally expired in January 1978, has been extended three times.

The union has said it will not negotiate with the board unless the contract is in force.One important aspect of the contract is that it provides for automatic dues checkoff on teachers' paychecks, the prime source of income for the union.

Rogers said he did not know what issues, if any, had been settled by negotiations for the board and the union.

While the talks were underway, the school system and the union continued making plans for a strike.

City school Superlntendent Vincent E. Reed said he would attempt to use substitute teachers and administrators in classes to keep schools open if there is a strike.

"You call as many substitutes as you can," said Reed, "and you try to keep as many classrooms covered as you can.... I would urge parents to send their kids to school. If we can't handle the situation, we'll make a decision about closing schools. But until we notify parents, we want parents to send their children to school."

At the headquarters of the teachers' union, printing orders were being made yesterday for picket signs.

The first step in arranging the strike is a meeting of teacher representatives from every school in the city, Fisher said.

Fisher said the meeting of the teachers' representatives will be Saturday at Metropolitan AME Church. At that meeting, Fisher said, plans will be made for organizing teachers by informing them about strike benefits, the progress of negotiations and how to set up picket lines at schools.

Fisher said he does not expect any resistance from teachers when the time comes to vote for a strike. He said the earliest date for the meeting, at which teachers will vote on striking, is Tuesday after Monday's George Washington's Birthday holiday.

The strike could begin as early as Wednesday, Fisher said.

The teachers' union does not have a strike fund. However, Phil Kugler of the national American Federation of Teachers, said his organization will pay the interest on all loans obtained by striking teachers during the walkout.

Among the major issues separating the board and the union are proposals by the board to increase the length of the work day and the work year for teachers. The board is also trying to limit the charges a teacher can use to begin grievance proceedings against an administrator.

In addition, board members have said they are trying to lessen the influence teachers have in the making of educational policy for the school system. The board has proposed removing from the contract provisions that give teachers a role in deciding procedures for evaluating teachers and grading and discipling students.