Declining student enrollment and budgetary problems have placed the jobs of 735 Montgomery County teachers in jeopardy, county school officials said last week.

Notices have been sent out to the teachers - all have worked in the school system less than two years - informing them thet they cannot be guaranteed jobs when schools opens in the fall, according to Kenneth Muir, school spokesman.

In addition, 25 school custodians will be terminated as of today as a result of the reduction of 493 positions called for in the fiscal 1980 budget, Muir said.

The country's problems are due in part to the anticipated loss of 5,000 pupils this year, bringing total enrollment to 109,334. Also, the fact that the Board of Education must find a way funding a 6 per cent cost of living increase for employees although the County Council approved a school budget that provides for only a 4 per cent salary increase, makes it probable that some teachers positions will be cut out, Muir said. Most of the $255.1 million school budget will go toward paying salaries.

The enrollment drop has left the school system with a surplus of 525 teachers for the upcoming year, according to Jack Hill, director of teacher personnel.

"Their (teaching) positions have been abolished, and they will have to be reassigned. But whether or not they are reassigned when depend on how many vacancies there are," Hill said. "It doesn't look as optimistic this year," he said, referring to the fact that the county was able to retain 120 teachers who were scheduled to be cut out of the budget last year.

Layoff notices went out to 1,000 "probationary" teachers in April since the teachers' contract requires that they be notified by May 1 if the county cannot guarantee their jobs for another school year. But this week, 265 probationary teachers were informed that they would be reinstated, Muir said.

The number of teachers who are rehired with depend on how many decide to leave the school system for one reason or another over the summer, Muir added.

John Fiscella of the Montgomery County Education Association said of the possible layoffs that "management has got problems: lack of money and lack of jobs. Seniority is the only fair way to determine who goes and who stays - cruel as that may be."

Fiscella said the teachers most likely to lose their jobs are in foreign languages, home economics or some of the vocational arts because of the declining enrollment in those areas.

The school system usually ends up with a thousand openings each new with school year, according to Fiscella.But the problem is that some of the surplus teachers may not be suited to teach in the fields where there are openings, he said.

"It's possible that some teachers even with a seniority advantage may not be rehired because of qualification problems," Fiscella added.