Washington teachers lost an estimated $8 million in salary last month during their 23-day strike, school officials said yesterday.

The officials said they want to use these unspent funds to provide makeup classes this spring and summer, and to give summer jobs to anout 2,000 graduating high school seniors.

In addition, the school system is expecting another $8.3 million in savings because enrollment is lower than expected and not all budgeted teaching jobs have been filled.

School Superintendent Vincent E. Reed presented plans yesterday to spend about $5.1 million of the expected surplus before the current fiscal year ends on Sept. 30. He said the remaining $3.2 million could be spent on equipment for long-term projects if the city council approves.

"I don't see this as a windfalls," Reed remarked in an interview. "The school system has always been short of funds. Now we have a chance to do some of the things we should have been able to do before."

The strike ended March 29 after a D.C. Superior Court judge met a key union demand and reinstated until July 15 the union's old contract, which the school board had sought to change.

Officials said then that strikers earning the average teacher's salary in Washington-$20,695 a year - had lost almost $1,600 apiece if they stayed on strike for the 23 days.

But there was wide disagreement between the union and the school board over the number of teachers who took part in the walkout.

Yesterday, James R. Boyle, the head of the school system's payroll office, said an average of about two-thirds of the city's teachers and other prolessionals whom the teacher's union represents stayed away from work during the strike.

Boyle saidabout 7,000 employes are represented by the union, including more than 6,000 teachers. The others, he said, are mostly counselors, librarians and school psychologists.

Yesterday, Deputy Superintendent Edward G. Winner said it was still impossible to give a firm total on the amount of money unspent because of the strike. He said the $8 million estimate was nearly all in salaries that strikers did not earn. But he said the school system also spent less than usual on substitue teachers, even though it had tried to hire more substitutes during the walkout.

Shortly before the strike ended, the union demanded that any makeup work scheduled this spring and summer be given only to those who lost pay because of the strike.

But Reed said no preference would be given either to teachers who took part in the striker or to those who continued working.

Yesterday, Winner said $1.5 million would be spent this spring on extra classes, starting Monday, that will allow about one-third of the city's 113,000 students to begin school an hour early or leave an hour late.

The six-week summer school session, which will start June 25, will enroll an estimated 25,000 students, Winner said, and employ about 1,000 techers. It will cost about $3 million.

Winner said it will be the largest summer session the District school system ever has run. For the past two years, he noted, almost all summer classes were cancelled because of budget cutbacks.

The planned summer job program for graduating seniors is the first the school system ever has funded, Reed said. He said he hopes most of the jobs will tie in with the students' academic interests and lead to regular employment later.

Many of the jobs will be with private employers or federal agencies. But Reed said the school system will pay $3.15 an hour to all students paraticipating. The total cost, he said, will come to $2 million.

Late Thursday the teachers' union filed a motion asking Judge Gladys Kessler of Superior Court to cancel or delay collection of $343.350 in fines she imposed for violations of her order against the strike.

The union said the fines should be considered by a court-ordered fact-finding panel that is making recommendations on a new long-term contract.

If the board presses ahead with collecting the fines, which are due on Monday, the union said negotiations for the new pact "will be seriously affected."