The District of Columbia Bard of Education, in a conciliatory move, proposed an "interim agreement" with the striking Washington Teachers' Union yesterday in an attempt to end the seven-day-old teachers' walkout that has severely disrupted city schools.

The board's proposal, which would provide for reinstatement of several sections of the union's former contract, drew a guarded response from the union. Union President William H. Simons said the offer "might be a basis of consideration for ending the strike," but he noted that it fell short of a compromise suggested last week by Mayor Marion Barry.

The school board's proposal prompted immediate resumption last night of talks between board and union negotiatirs. The talks began shortly after 8 p.m. at Federal Mediation and Conciliation Service headquarters and were still under way well past midnight.

Simons said before the negotiating session began that teachers probably would not return to work before Monday, even if last night's talks led to an agreement to end the strike.

Last night's meeting -- the third bargaining ession since the start of the strike March 6 -- was announced as the union conceded that an increasing number of teachers had begun to return to work in the face of a Superior Court judge's contempt decree and imposition of steep fines on the union.

Simons said 82 percent of the city's public school teachers stayed off their jobs yesterday -- a drop from the 89 percent the union had previously claimed. "We did have some slippage, which I admit," Simons said. School officials, whose estimates have differed sharply from the union's, said yesterday that 47 percent of the school system's more than 6,000 teachers were at work -- the same percentage they reported Tuesday.

About 53 percent, or nearly 60,000, of the 113,000 city public school students attended school yesterday, according to school officals.This was the same estimate as school officals gave Tuesday. A tour of several schools yesterday by a Washington Post reporter indicated that junior highs were offering some basic English, mathematics, science and gym classes, but that senior highs were providing no regular classroom instruction.

A total of $23,100 in fines had accumulated against the teachers' union and its leaders by yesterday as a result of the contempt order handed down Monday by Superior Court Judge Gladys Kessler. The union has not been required to start paying the fines. Under Kessler's order, the fines will increase markedly from day to day. For example, if the strike continues through Friday, the total owed would reach $76,600.

Yesterday's proposal by the Board of Education appeared designed to offer legal protection for teachers against possible reprisals for their participation in the strike in exchange for their agreement to return to work. In a statement issued after its midafternoon meeting, the board said its proposal would "insure to individual teachers the protection of due process."

In addition, the board's chief negotiator, Kenneth W. Nickoles, said at a news conference that the board was prepared to "make some changes in our stated position" on some issues, including the board's previous proposal for a longer school year and school day. Nickoles declined to say specifically how the board would alter its proposal.

The school board's offer yesterday would reinstate provisions of the union's former contract that deal with disciplinary action against teachers, grievance and arbitration procedures and involuntary transters of teachers from one assignment to another.

The proposal did not, however, include reinstitution of the old contract's dues checkoff provision. That provision permits the union to collect about $59,000 a mopnth through payroll deductions. The checkoff collections form the bulk of the union's income.

The board's plan would also not reinstate serveral other provisions protecting teachers and union rights set forth in the old contract and sought by the union in return for ending the strike.

These include provisions recognizing the union as the sole bargaining agent for the teachers, preventing assignment of teachers to nonteachig duties, protecting union workers from harassment in performance of union duties and sections governing the issuance of paychecks to persons on leave.

Yesterday's action was taken "by consensus" at a two-hour closed meeting of the board, the second board meeting in the last three days. The two meetings are the only ones the board has held since the strike began.

The proposal represented a sharp departure from the board's previous policy of hoping that a contempt-of-court order, with its accompanying heavy fines, would drive the union back to the bargaining table and return most teachers to the schools.

"We did not expect it to stop the union from calling for a strike. However, we did expect a greater percentage of people to return to the classrooms," said board member R. Calvin Lockridge (Ward 8). "When they didn't, we had to look at other proposals."