A school board plan for an interim agreement to end Washington's two-week-old teachers' strike was rejected last night by union leaders, who denounced the proposal as "a demand that teachers surrender."

"They want the teachers to crawl back [to work] with their fails behind their backs and take any crumbs that fall off the table," Washington Teachers' Union President William Simons said yesterday after two days of negotiations on the board plan. "They really should know by now, that's never going to happen."

Federal mediator James R. Williams said negotiations would resume this morning even though almost no progress had been made in the new round of talks.

"We have no try to find some way to end this strike," Williams said, "but I don't know how we're going to do it. We're looking for a solution to a situation that's almost insoluble, but we have to try to find a way to do it."

The board plan, which was patterned after a proposal made earlier by Mayor Marion Barry, called for teachers to go back to work immediately in return for reinstatement of several key provisions of the union's former contract. After that, efforts would resume to reach a long-term contract settlement.

But Simons said last evening that teachers wanted to reach a long-term agreement now, based on union proposals first made on Sunday for major pay and benefit increases before returning to work.

He suggested that the only way to get the talks moving productively again would be for school board members themselves to take part in the negotiations, rather than continuing to have school administrators do all the negotiating for them.

Yesterday, Barry made a similar suggestion that board members get more directly involved in the talks. But last evening a majority of board members continued to reject the idea on the grounds that the board was too divided and too vulnerable to political pressures to bargain successfully.

Barry was described yesterday as increasingly concerned about the lack of movement in the negotiations.

The sources said Barry is concerned that, if the strike continues, it may be viewed by members of the city's organized labor community as an example of an attempt to break the teachers' union. That kind of feeling, the sources said, could prompt other unions to become more actively involved, thereby intensifying the strike's crippling effects.

"It probably has passed the point where it could have been settled," one Barry intimate said. "It's at another level, and it has to be settled soon.

"At one point," this source said, "the union would have accepted the [compromise] proposal. But the board stayed out and the union came back with a longer laundry list. They said they now have to have something more, because people can't lose a month's pay and go back to work for the same thing they had when they went on strike."

Barry met with half a dozen of his top aides until early yesterday morning discussing what to do next about the strike. He also briefed City Council members about possible legislative actions to be taken.

Barry gave the council a proposed resolution asking the board to become directly involved in the negotiations instead of filtering its views through the school board negotiators, who are members of the staff of School Superintendent Vincent E. Reed.

Barry also asked that a resolution be passed urging the mayor to become directly involved in bringing both sides together, one source said. The source said the council refused to act immediately on Barry's request, preferring to wait until it could meet first with members of the school board.

The mayor and several of his top aides met for more than two hours Tuesday night with Simons, other local union leaders and Bob Bates, a representative of the American Federation of Teachers, with which the local union is affiliated.

"It was clear from that discussion," one source said, "that the union is taking a harder line and they are prepared to see it out in terms of the fines, the firings, the involvement of other unions and the involvement of the national leadership... What really came through is that it could be that Bill Simons is no longer in control and that is very disturbing."

Sources said Bates did more than 75 percent of the talking in the meeting and often, gesturing with his hands, would cut Simons off in the middle of discussions.

Yesterday morning the board's chief negotiator, Kenneth W. Nickoles, charged that the American Federation of Teachers, rather than the Washington Teachers' Union local, "now is in control of these negotiations" and was responsible for the increase in union demands.

Nickoles said that ever since Bates joined the negotiations on Saturday the union has been "attempting to make a whole new ball game, and that is causing problems."

Simons strongly rejected Nickoles' charge in an interview later, saying, "William Simons has been and is the union's chief negotiator... I always have run the show and anybody who thinks to the contrary has another think coming."

In another development, the school board asked D.C. Superior Court Judge Gladys Kessler to begin enforcing her order against the strike by starting to collect fines today from the teachers' union and its leaders.

In court papers, filed by acting D.C. Corporation Counsel Louis Robbins, the board said that fines now due total $416,025.

School board members said the back-to-work proposal offered Tuesday was designed to meet teacher fears that if they return to work without a full contract they would be subject to arbitrary action by administrators.

Ten days ago the board had spurned a similar plan when it was first offered by Barry, and the union said it was "receptive."

Simons declared yesterday, however, that "a lot of circumstances are different now." He said the teachers now wanted to reach an agreement until Aug. 31, 1980, and including major salary increases plus free insurance for medical, dental and optical care.

The board has rejected these expanded demands as being beyond its legal authority because the board will not have the power to negotiate salaries and benefits until 1980.

Salaries are now set by the mayor and City Council and are reviewed by Congress.

Just an hour before negotiations ceased at 6:30 p.m. yesterday, Nickoles said the board wanted to change one part of its interim plan and begin fact-finding procedures immediately on all major issues still unsettled.

Originally, the board had suggested that fact-finding begin only after teachers returned to work and four more days of around-the-clock negotiations were held.

Simons told reporters an hour later that the union had rejected this revised proposal along with the rest of the board's interim plan because it wants its expanded demands to be considered as part of any procedure for reaching a new contract.