Montgomery County Executive Charles W. Gilchrist yesterday proposed a $598.5 million county budget for next year that would mean an increase of less than $25 in the average property taxpayer's bill.

The central element of Gilchrist's "hold-the-line" budget is a 34-cent cut in the overall property tax rate. The proposed cut, the largest such decrease in 20 years, would almost offset an expected 12.5 percent average increase in the assessed value of property in the county.

Budget Director John Short said yesterday that the proposed spending level answers the citizen's demands for "belt tightening" without making major cuts in existing county services.

Reversing a 15-year trend of government growth in one of the nation's wealthiest counties, Gilchrist's proposed budget would cut back on the county work force, eliminating 42 positions now vacant.

The proposed budget's effect on property tax bills in the county can be estimated only in general terms. This is because tax bills reflect both the county tax rate -- which averaged $3.58 per $100 of assessed valuation but varies from area to area depending on the level of services -- and the assessed value of property.

The tax rate, set by the county, and the assessments, established by the state, are computed at different times of the year, making impossible any exact comparisons of countywide increases in tax bills.

Under Gilchrist's proposed budget, the tax rate would average $3.24 per $100 of assessed valuation.

Gilchrist said that the budget "reflects the taxpayers' message... to curb expenditures of public funds without using a 'meat ax' approach to services."

Last November voters approved a charter amendment requiring that the annual rate of increase in county budgets not exceed the rate of inflation, which this year is 8.7 percent. However, Gilchrist's proposed increase is substantially less than that: 4.8 percent.

If approved by the county council, the budget would drastically alter a 10-year pattern of budget increases that have averaged about 11 percent.

Gilchrist's task of keeping down taxes without slashing services was made considerably easier by a muber of revenue windfalls in this fiscal year, including an unexpected $12 million surplus from taxes on housing sales and high interest rates, which allowed the county to earn a "record interest income on investments."

Gilchrist cautioned, however, that these windfalls are unlikely to come the county's way next year, because of projected slowdowns in housing sales.

"If it becomes necessary in future years to increase the tax rate, then the burden probably will be on us to prove to the citizens that the increase is necessary," the executive said.

One of Gilchrist's major cuts was in the proposed budget of the county's Department of Social Services, largely because of a decrease in the number of welfare clients.

For example, the average monthly caseload for aid to Families with Dependent Children dropped from 119 to 77 from last year.

"I'm sorry to see that," Gilchrist said. "It means that people who need help can't afford to live here."

In addition, libraries will be closed Friday evenings, the lowest use time, for a savings of $63,000, and the Four Corners Library, which has been proposed for closing several times over the past few years, will be shut to save $76,000. One county-run liquor stor also will be closed.

Of the total of 42 positions cut from the 5,300 central government work force, 28 were in health and social services.

Gilchrist has funded fully the 6.5 percent cost-of-living pay increase for these employes, meeting the requirements of a bill passed last year to guarantee pay increases equal to three-quarters of the Consumer Price Index increase.

Among other new items in the budget are:

Countywide installation of a computerized voting system.

Full implementation of the police take-home car program.

Construction of a new police station in Germantown.

A 28 percent increase in day-care services.

The police department also will implement an $820,000 career development program, a comprehensive and controversial system of training and granting promotions originally proposed by ousted Police Chief Robert J. diGrazia.

That program has been substantially revised by diGrazia's temporary successor, Maj. Donald E. Brooks, and will, among other things, include a one-rank promotion for most police officers.

Further, Gilchrist propses to increase book purchases in county libraries by 11 percent at a cost of $740,000.

In sending the proposed budget to the council, Gilchrist passed on without comment a $281,5 million school budget, which represents a 3.9 percent increase over current school expenditures.

Superintendent Charles M. Bernardo had recommended a $287 million program, which the school board has already whittled down to $284.2 million. But the council has asked for a budget no higher than $281.5 million, a figure Gilchrist has said he considers "adequate." Gilchrist said yesterday he may recommend further school budget cuts in the next few weeks.

Council President Neal Potter said that he "suspects" the council may cut the school budget even more. He also commended Gilchrist for recommending a budget "2 percent lower than we'd hoped for."

But council member Rose Crenca, a proponent of the tax-butting charter amendment TRIM that was narrowly defeated in November, said she "doesn't know whether to be angry or delighted or both."

Gilchrist's tax cut is only three cents higher than the one TRIM would have mandated. "What was the big deal about TRIM and how awful it was?" she said.