The District of Columbia Board of Education, seeking to end the two-week-old public school teachers' strike, disclosed last night that it will offer the teachers' union today a new proposal patterned on recent recommendations by Mayor Marion Barry.

How the striking Washington Teachers' Union will respond to the new offer was not immediately clear. Union President William H. Simons said last night, "I would not like to make a comment until I see it." At a news conference last night, Barry also said he was "not sure what the union's reaction will be."

Negotiators for the school board said they plan to make their offer to the union at a bargaining session this morning at Federal Mediation and Conciliation Service headquarters.

Barry's proposals for settling the strike, as the mayor noted last night, had initially been accepted by the union, but they were rebuffed by the school board. Since then, however, the union has sharply escalated its demands by calling for substantial increases in salaries and fringe benefits for teachers -- an economic package largely outside the scope of Barry's proposals.

Nevertheless, union President Simons indicated some flexibility in an interview yesterday afternoon -- before the new school board proposal was made public. "There are some immediate objectives that would end the strike, and then we'd go on from there," he said. "We are rethinking our position."

Under Barry's most recent recommendations, made public Sunday, the union and the school board would conclude a temporary agreement to end the strike and allow bargaining to continue on many issues still in dispute. The temporary accord, as outlined by Barry, would prohibit reprisals by school officials against teachers who took part in the strike and would reinstate some key provisions of the union's former contract, including those dealing with grievance procedures.

Barry's plan provided for four days of around-the-clock negotiations in an attempt to settle other disagreements. Unresolved issues would then be submitted to fact-finding panels for further recommendations. Barry's proposal did not provide for reinstatement of the checkoff -- automatic payroll deduction of union dues. The checkoff is a major source of union funds, yielding more than $70,000 a month in dues, according to school officials.

The school board's new offer was announced after a series of closed board sessions that continued throughout the day and early evening. Although the board's chief negotiator, Kenneth W. Nickoles, declined to divulge details of the offer, it was described later by several board members.

"It's basically the mayor's proposal with minor modification," said board Vice President Carol L. Schwartz. Mayor Barry also referred to it as a "modified version" of his plan. One key modification, board members said, would be aimed at prohibiting reprisals only for participation in the strike and would not bar disciplinary action against any teacher found to have engaged in violent or other improper conduct during the walkout.

The union's "escalated" demand on Sunday for salary and benefit increases was immediately rejected by school officials. The school board does not currently have legal authority to bargain over wages. although newly enacted legislation will give the board such bargaining powers next January.

In an attempt to exert pressure on both sides, Wayne L. Horvitz, director of the Federal Mediation and Conciliation Service, met separately yesterday with D.C. school officials and with union President Simons.

Horvitz urged the union and the school board to intensify their efforts to end the walkout and named a mediation service representative, James R. Williams, to take part in the negotiations. Williams will join two other veteran federal mediators, Gilbert S. McCutcheon and John A. Wagner, who have been participating in the talks.

Under a contempt-of-court order handed down last week by Superior Court Judge Gladys Kessler, the union and its leaders as of yesterday faced fines totaling $114,750. The fines, which the union has not yet been required to pay, will increase to $160,500 today.

Kessler has scheduled a court hearing for 2:30 p.m. today on a request by school officials for a preliminary injunction prohibiting the walkout. Such an injunction would replace a temporary restraining order granted by Kessler shortly before the start of the strike March 6.