Montgomery County Executive Charles Gilchrist proposed a $724 million budget yesterday that would hold the real estate rate at its current level, but give most property owners substantially higher tax bills because of rising assessments.

The budget for the fiscal year that starts July 1 would eliminate 200 county jobs and concentrate on completing existing projects rather than starting new ones.

"This really is not a time to fashion and implement large new programs," Gilchrist told reporters gathered for a briefing in a Rockville conference room.

County offices concerned with health, social welfare and transportation would by hardest hit by the personnel reductions, though Gilchrist predicted that enhanced productivity would reduce the impact on the public in most cases to "inconvenience."

At the same time, he proposed adding 14 officers to the police force to combat growing crime and giving county employes an 11.4 percent salary increase.

The average property owner will still pay taxes at the current rate of $3.50 per $100 of assessed valuation, including special rates for storm drainage, fire protection, parks and other services. The reason most homeowners will get larger bills this year is that the bills are based on assessments, which continue to soar with the property market.

Thus the tax bill for a house with a market value of $100,000 that got its triennial reassessment two years ago would rise from about $1,780 last year to $1,920 this year.

If the house was among those reassessed last year the jump would be from $1,570 to $1,800. For the third group of properties, to be reassessed next fall, the tax bill would stay about the same at $1,565.

It was the third year in a row that Gilchrist had preached fiscal restraint in his draft budget, which is scheduled to go before the County Council today. The budget has already prompted skepticism among some council members that 200 of the county's 5,000 jobs could be eliminated without serious deterioration in services.

Gilchrist's framework could also be distorted by state and federal lawmakers now searching for ways to cut their own budgets.Contributions from outside the county are supposed to cover almost 20 percent of the expenditures Gilchrist outlined yesterday.

Gilchrist's budget is 8 percent higher than the current year's. He defended the rise in spending by pointing out that it would be well behind the 12.5 percent jump in the consumer price index measured last November.

Health and social service agencies would lose 96 positions. These would include 15 day-care workers at a Takoma Park facility that will be phased out, two nurses at Montgomery College and three health assistants in the county medical system.

Transportation offices would lose 37 slots. Hours at the county's 19 libraries would be curtailed and two jobs eliminated. Gilchrist said he expected that perhaps 50 persons would actually be fired as a result of the staff reductions. The rest would be transferred to other county jobs coming open through attrition. He noted he was targeting an additional 100 jobs for elimination in the follwoing fiscal year.

The county executive also sought a $3-million cut in $336 million requested last month by the school board, the largest user of county funds. His planners had not had time to determine where to recommend such cuts.

He also promised to save money through conserving fuel used by county offices and vehicles, integrating certain offices, installing word processing equipment and creating an "employe evaluation system" in every department.

To a few areas, Gilchrist wants the county to give more than the average increase in funding. Pointing to a rash of robberies and burglaries in 1980, he is seeking an 11 percent rise in the police department's outlay and creation of 14 new positions to bring the force to 789 officers.

About 40 percent of the revenues required for Gilchrist's plan would come from property taxes. While he proposed lowering the county property tax rate by four cents per $100 of assessed valuation, that would be offset by raising the mass transit tax rate by four cents.