Metro General Manager Carmen E. Turner yesterday recommended a $425 million operating budget for the next fiscal year that holds the line on bus and subway fares.

Turner described the spending plan as "probably the tightest budget" ever drawn up by the transit agency.

Under Turner's proposal, bus and rail fares, which were raised June 30, would not be increased again before June 30, 1986, the end of the next fiscal year. In the last increases, minimum rush-hour fares rose a nickel to 80 cents and surcharges were revised for long-distance rail trips.

In moving to forestall another increase, Turner fulfilled a pledge she made earlier this year, when she warned that fares should be kept "affordable" to encourage ridership.

Her plan appeared likely to win solid backing from Metro's board of directors, which has expressed concern about rising fares.

"Unless something drastic were to happen, I don't think there will be any fare increase," said Metro board Chairman John G. Milliken, who also is vice chairman of the Arlington County Board. He praised Turner's proposed budget, saying it would "cut back significantly on overhead and administrative expenses."

The budget recommendations are expected to be reviewed by the Metro board, which plans to take final action by March.

Turner relied largely on cost-cutting moves, including eliminating 52 jobs, to avoid a fare increase. Milliken said two of Turner's recommendations would likely stir considerable debate.

One of these proposals is a $1.5 million reduction in bus service on what were termed "marginal" routes with relatively few riders.

Officials said that "a couple dozen" bus routes were targets for possible cutbacks, but declined to identify them. Previous moves to cut bus service have drawn protest.

Under another proposal, Metro's staff of telephone information workers, who answer calls from patrons about routes and fares, would be slashed from 57 employes to 33.

Officials said improved training and equipment would offset the cutbacks, but the issue previously has raised concern.

The transit system's mounting costs long have drawn complaints from local governments, which furnish more than $200 million a year to offset Metro's deficits and pay off interest on bonds. Metro officials said Turner's plan marked a significant curtailment in costs and subsidies.

The costs of running the bus and rail system would rise from an estimated $399.1 million this year to $424.9 million under the proposed budget.

Despite the increase, Turner said the financial trend "is down" if it is viewed "from a constant dollar standpoint which factors out inflation."

Subsidies provided by county and city governments would increase from an estimated $208.4 million this year to $222 million next year.

The 6.5 percent increase appeared to be among the smallest since the Metro system was established in the 1970s.

Officials initially argued that the proposed rise in subsidies would be "the lowest dollar and percentage increase" in Metro's history, but their assertion was not borne out by a review of earlier data. They also described it as a 4.2 percent increase by citing figures that have since been revised.

Turner said she planned to trim Metro's staff of more than 7,600 employes largely by leaving vacancies unfilled and through resignations and retirements.

The curtailment reflected a 5 percent cutback in administrative overhead, increased automation and other moves to improve productivity, she said.

Turner proposed to hire 125 rail employes to prepare for the opening of an Orange Line extension to Fairfax County's Vienna terminus, scheduled for mid-1986, but this increase would be offset by eliminating 177 positions for clerical and other workers.

Turner also suggested reducing electric power consumption by running some trains at slightly lower maximum speeds. To avoid delays for passengers, she said these trains would also reduce waiting time at stations. The plan "would certainly not in any way degrade service," she said.