County Manager W. Vernon Ford proposed a $150 million budget to the Arlington Board yesterday for the year beginning July 1. It calls for increasing the water-sewer rate by 20 percent, keeping real estate taxes at existing rates, and giving a 7 percent across-the-board salary increase to the county's 2,500 employes.

Ford said the utility rate increase would raise the average homeowner's bill by $21 each year, but that the county property tax rate could remain at $1.49 for each $100 of assessed value.

Even so, most Arlington homeowners will pay higher real estate taxes this year because property values are expected to go up about 8 percent, and assessments rise with them.

Last year the county board reduced the real estate tax rate slightly, and several board members have predicted recently that they may be able to cut the rate again this year when final budget is passed on May 13.

Ford's proposal is up 6 percent over this year's budget, and its largest singel item is for schools. The $36.2 million proposed for schools is nearly indentical to the amount of county money the schools are spending this year.

School Superintendent Larry Cuban had asked the board for $38.1 million, and school officials have repeatedly characterized funding levels in recent years as inadequate and unfair.

The largest proposed increase in the budget this year is for Metro.Ford's budget contains $5.5 million for the regional subway and bus system - a 62 percent increase over this year.

Part of the dramatic increase was necessary to cover an underestimate of how much the system would cost this year, according to Anton S. Gardner, fiscal analysis chief of Arlington. Also, included in this time, however, is money allocated to pay for the possible expansion of the subway system to include evening and Saturday hours.

The budget, presented in shopping list form with options for minor increases and reductions in programs, is balanced, as it must be by state law, and is "at or near the lowest acceptable level of services," Ford told the board.

Included are options for cutting Sunday hours in half at Arlington's Central Library, the most heavily used library in the state, by closing at 5 p.m. Another option would be to reduce hours at the county's six branch libraries by having them open only 40, rather than 48, hours a week.

The budget also includes a proposal to cut back free after-school and summer recreation programs at seven schools and recreation centers. County budget officials say that although these programs are popular they are of lower priority than some other items because of the county's declining youth population.

Ford also proposed two modest new programs totaling $100,000 designed to improve the county's image and lure businesses and residents through a marketing and public relations effort.

Ford's $150.5 million budget projects receiving $31 million from state and federal sources and the rest from Ar- lington residents Of the latter amount, $56.6 million is expected to come from the real estate tax.

About $58 million of approximately $119 million in county-generated revenue would be spent under Ford's proposal, for general services, which include the police and fire departments and the departments of human resources and community affairs.

Ford said that staffing levels in all departments would remain virtually the same. Of the $57.6 million, $10 million would go to the police department with possibility that the board may make slight reductions in the staffing of the burglary investigation squad and crime prevention patrol. In the event that the board cuts any position the county would attempt to find another job for the employe, Ford said.

The Department of Community Affairs, which oversees parks, recreation and planning would receive $8.6 million, a slight increase over last year.

The Department of Human Resources, which receives the bulk of its funds from the state and federal governments, would get $2.9 million from the county and a possible addition of two social service workers to handle the increasing number of elderly applicants.

Ford's budget also allocates $2.7 million to pay for the proposed 7 percent pay raises for county employes.

Of the $155.9 million in Ford's proposed general fund budget the largest amount, almost $58 million, would pay for county services at the following levels: about $17 million for police and fire, $10.3 for administration, $8.6 million for community affairs, including parks and recreation, and $8.6 million for public works. The remaining $13 million will be apportioned among the department of human resources ($2.9 million), libraries (almost $2.4 million), and other departments.

After county services, other major expenditures in descending order are $36.2 million for the schools, $6.1 million to pay off debts, $5.5 for Metro and $22 million for a capital budget that includes possible acquisitions of park land and development of bike trails.

Although most board members said that they haven't yet had time to study the budget, several indicated thaty they were pleased by its austerity. But Chariman John W. Purdy said he was "concerned that we're talking about a total budget that is substantially less than the school board asked for."