Arlington County Manager Larry J. Brown proposed a $260.9 million budget for fiscal 1986 yesterday that represents a 6.2 percent increase over current spending but would require no increase in the real estate and personal property tax rates.

The budget, presented to the County Board last night, provides for 4 percent raises for both county and school employes, $53.9 million in school operating funds, $1 million for school capital projects, and -- for the first time -- a reduction in the county's share of Metro transit costs, which will drop by $2 million to $10 million.

Brown noted that there is growing uncertainty over continued federal aid, but he said the impact of any cuts in the fiscal year that starts July 1 will not be substantial. There would be "a significant impact" in the following fiscal year, he said, particularly if revenue-sharing is eliminated and community development funds are sharply curtailed.

The county is expecting $10 million in federal aid in fiscal 1986, an amount basically unchanged from this year. Another $25 million is expected in state aid, but the exact total will not be known until the General Assembly adopts the next state budget.

The county is in the process of rebuilding its $5 million general reserve fund to help offset any major cuts in federal aid in future years. That fund was depleted recently when the county had to pay a $5 million court judgment stemming from an Arlington police chase of robbers into the District of Columbia in which a bystander was severely injured. Last week the board restored $3.3 million to Arlington County Manager Larry J. Brown the fund and the proposed budget suggests adding another $2 million.

The proposed budget is based on a projected growth of 9 percent in real property assessments this year and 8.5 percent next year. Brown said several new building projects -- such as two major shopping centers at Pentagon City and Ballston and a government-commercial-residential complex at the courthouse -- are pushing development to a "record pace."

The current real estate tax rate, the major source of county revenues, is 97 cents per $100 assessed value, the lowest of any major jurisdiction in the Washington area. If the rate remains stable, as the County Board has said it will, the average $116,000 house this year will jump 6.5 percent in value to $123,500 next year, and the tax bill will rise $75 to $1,198.

The personal property tax, levied on office equipment, cars, boats and planes, is at $4.75 per $100.

Brown characterized his spending plan as a "continuation budget" that will enable the board to carry out its goals for community improvements ranging from extra services for the non-English-speaking population, to increased fire protection measures, activities for senior citizens and health services for the mentally ill and victims of family violence.

Separate from the budgeted improvements is a "wish list" of 23 other programs totaling almost $1.9 million that the board may want to finance. They include starting up a mechanized trash-collection system similar to the District's, increases in housing and tax-relief benefits, and two more school nurses.

Of the proposed $260.9 million, Brown is seeking $215.3 million for general operating funds, a 4.9 percent increase over this year. The rest of the budget comes from special self-sustaining funds, such as that generated by water-sewer user fees, and noncounty school revenues. While there are no scheduled increases in water-sewer or residential refuse user fees, Brown has recommended a 10 percent increase for commercial trash-disposal fees.

The proposed budget calls for $9.7 million in capital projects, a 28 percent increase over last year. They include the purchase of land for a new fire station for the Columbia Pike corridor, a new emergency telephone-answering system, and improvements to the Clarendon streetscape and county jail. The proposed budget also calls for a net increase of 21 county employes, nine of whom would be firefighters to staff the new equipment bought for the Crystal City fire station this year.

Other budget features include a community activities fund of $2.3 million, used to finance joint county-school facilities such as the Thomas Jefferson Intermediate School/Community Center. Debt service is budgeted at $16.7 million.

The board has scheduled a public hearing on the budget for 7 p.m. March 12 at Kenmore Intermediate School. Budget adoption is scheduled for April 27.