In a last-minute effort to avoid a teachers' strike the Washington Teachers Union and the D.C. school board are scheduled to meet today for a final negotiating session before the old contract between the board and the union expires at midnight.

On Monday night the board voted against extending the old contract, which originally expired in January 1978, for a fourth time. Union president William Simons has said repeatedly that his union members will strike if the contract -- which provides for union dues checkoff on teachers' paychecks -- is not reinstated for the duration of negotiations.

"The position of the teachers was made clear in October," said Simons, referring to a union membership vote to strike if the contract was not extended at that time. The strike was averted in October when the board phoned a union rally the night before the strike was to have started to say the contract would be extended.

"We will not work without a contract," Simons said. "I expect that will be the position of this union again. The building representatives (who are elected by teachers at each school building) met last Saturday and they said they would not work without a contract."

Simons said his union could get strike authorization from its members in a matter of hours.

"It won't take much," he said. "Teachers are in a state of readiness for this."

Simons said he has not been formally told of the board's decision against continuing the contract. He said he will ask the board's negotiators today if the board's decision is final.

Minnie S. Woodson, president of the school board, said yesterday the union has enough time, in today's negotiation session, to agree to proposals that would avert a strike.

"There is plenty of time for the negotiation process to continue and come to a resolution of the entire problem if that is desired," Woodson said.

Woodson said it is "in the interest of the union" to have the old contract extended again and again because the contract is very favorable to the union.

"Our prime motivation is to improve education in the city," said Woodson, a former teacher who quit the union because she had ideological conflicts with its leaders. "Our hands are tied because of things other boards agreed to in the past. We would bt delinquent if we allowed this to go on."

Woodson said teachers in the city's public schools should read the contract proposals made by the board and decide for themselves if the board is being unreasonable.

Woodson said, "If any teacher reads the proposals, and I don't know how many have taken the time to read them, I think they would say that is is a very good working draft and we should be able to work from that and come up with a contract. Our contract (proposals) only took out policy matter that the board should be responsible for and not the union."

Board members have said they want teachers and the teachers union out of the decision-making process for the school system. To limit the union's in fluence in the shaping of school system policy the board has proposed eliminating several provisions of the existing contract.

For example, the board wants removed from the contract the procedure for evaluating teachers. Under the current agreement the union has direct input into the board's procedure for evaluating teachers. The board wants to decide how teachers will be evaluated without any input from the union.

In addition, the board wants the union and teachers to be excluded from making decisions on how students will be disciplined and graded.

Although the pay scale for teachers, which is decided by the City Council and Congress, is not an issue in these negotiations, board members frequently note that public school teachers in the District are the highest paid teachers in the metropolitan area. And the board members compare the teachers high salaries with the low scores achieved by D.C. public school students on standardized national tests.

To get teachers to work harder the board is proposing to the union that teachers work a longer day and a longer school year. And, under the board's proposals, the grievance procedure, by which teachers complain about administrators, would be limited to specific violations of the contract between the teachers and the board.

Meanwhile the teachers' union is proposing that the teachers be given more authority to set policy for the school system. For example, the union is asking that teachers and students be required to have special training before they can be placed in "open space" schools.

The highlights of the union's proposals to the board include: easing the requirements that allow teachers to transfer from school to school to allow for "hardships," such as teachers who cannot get along with administrators at their schools; an "agency fee," that would require all teachers to pay union dues, even nonunion teachers, and a requirement that a substitute teacher be hired for every absent classroom teacher to prevent one teacher from having to handle two classes when a teacher is absent.