Fairfax County Executive J. Hamilton Lambert proposed a $1.25 billion budget yesterday that avoids raising taxes but recommends an array of new county facilities and programs in fiscal 1986 to be funded with the help of sharply higher revenues generated by the county's growing business community.

County supervisors, citing those higher revenues, immediately pledged to slash Lambert's budget and cut the county's real estate tax rate of $1.46 per $100 of assessed value by 3 to 12 cents.

"There's no doubt in my mind that we can provide a tax cut of considerable proportions," said Supervisor Joseph Alexander (D-Lee).

"I think [Lambert] wanted to let the supervisors make the cut," said Supervisor Thomas M. Davis III (R-Mason).

The county has been running a budgetary surplus of several million dollars in the current fiscal year, largely due to increased county taxes generated by a booming local economy, county officials said.

Flanked by a retinue of budget advisers and smiling broadly at a press conference yesterday, Lambert cited the county's "superb" financial health and declared: "We are providing tremendous expansion in service."

The county executive's budget, which calls for higher fees for trash and leaf collection and sewers, and a decrease in telephone utility taxes, proposes a 10.1 percent spending increase in the general fund -- the largest in three years. General fund spending, which does not include public school expenses, would rise to $789 million from the current level of $716.5 million.

One of the largest new spending chunks recommended by Lambert, and the one likely to be the most controversial, would provide $14 million for construction of sewers, water lines and roads for the county's proposed government complex along I-66 near Fair Oaks Mall.

The complex, which would cost more than $55 million, has long been on county planning charts but has never been submitted to voters in a bond referendum. Several supervisors said yesterday that the $14 million spending plan would be a likely target for cuts when the board prepares to adopt a final budget in April.

"I don't think it's a priority for the government to spend its money on developing property," said Davis, who has long opposed the complex.

Other supervisors who support the plan, including board vice chairman Martha V. Pennino (D-Centreville), have said it would save Fairfax more than $2 million it now spends yearly to rent private office space. "I look upon [the $14 million] as an investment," Pennino said.

The budget proposed by Lambert also includes a 4 percent cost-of-living raise for the county's 7,900 employes. Total increased compensation for county workers, not including school employes, would come to about $12.2 million.

Of the 246 new county employes recommended in the budget, about half would staff new or expanded facilities, according to Lambert. Among those new facilities funded in the budget would be six new day-care centers, including one for the handicapped; a $3 million community library in the Fair Oaks area; a $1 million, 36-bed residential home for mentally ill adults and a $772,000, 16-bed facility for the mentally retarded.

County officials said the facilities for the mentally ill would help to house more than 100 people currently on a county waiting list.

Lambert's budget also would fund a new $2.6 million feeder bus station in Huntington, two new pedestrian overpasses at Routes 50 and 123 and an $8 million county warehouse in the Edsall Road Industrial Park.

For the board to cut the real estate tax by 5 cents, it would have to eliminate more than $15 million from Lambert's proposed spending package. Each penny on the tax rate equals about $3 million in county revenue.

Asked yesterday whether he knows that supervisors are eager to cut taxes, Lambert smiled and said, "I've heard that rumor." Some supervisors said that in proposing a budget with no change in the real estate tax, Lambert was intentionally leaving the political glory of a tax cut for them.

Supervisors also said they thought the economy is strong enough in the county to guarantee that taxes will not rebound next year.

"We're not going to play games with this budget and lower the tax rate one year and raise it the next," said Republican Board Chairman John F. Herrity.

Lambert warned in his budget message, however, that despite Fairfax's rosy financial picture, proposed federal budget cuts could hurt the county in the future. He cited revenue sharing funds, mass transit subsidies, and school lunch programs as areas threatened by federal reductions.