Virginia Gov. John N. Dalton's administration yesterday took a frist tentative public step toward proposing a dramatic increase in state aid for Metro.

State Transportation Secretary George Walters suggested, in effect, that Metro be treated like a highway project. Walters, in an appearance before the State Highway and Transportation Commission in Richmond, outlined an "idea" under which the state would assume 95 percent of the remaining Virginia cost of building Metro.

That would include the $3 million Virginia share of retiring Metro's revenue bonds, as have which increases to $7 million in 1983. It would also include the $12.9 million in debt service on local bond issues that Alexandria, Arlington, Fairfax County and Fairfax City have sold for Metro construction money.

The percentage -- 95 -- is the same that the state presently assumes in county highway projects.

Walters stressed in a telephone interview yesterday that the "idea" -- he declined to call it a formal proposal -- had been discussed with Dalton, but that did not mean the governor endorsed it. Futhermore, the idea comes without the revenue-raising tax that would be necessary to make it work. Under the ideas, Walters estimated, Virginia aid to Metro could rise from the $10 million Northern Virginia now receives to $18 million next year and then increase to $34 million in 1986.

The idea does not contain an offer of state assistance for Metro's mounting operating costs -- an item that Virginia governors have traditionally insisted is a local responsibility.

However, according to the way Walters explained the proposal to several Northern Virginia legislators yesterday, it is assumed in Richmond that if the state picks up most of Metro's capital costs, the relieved local governments can pledge their existing tax revenues to fund Metro's operating budget. Thus, the "stable and reliable funding source" that the federal government is requiring of local governments as a price of continued federal participation in Metro, would be guaranteed.

Paul G. Edwards, Dalton's press secretary, was asked if the governor supports the idea. "Not yet," Edwards said. "The governor has the full range of options open to him."

It is understood that those options include various increases in the present state gasoline tax or titling taxes. Dalton has consistently said that he opposes tax increases, but events in the highway construction and maintenance program are making that a difficult position.

That is because there is a $52.9 million shortfall this year in Virginia's planned highway maintenance and construction program. Most of that shortfall results from the fact that the state's 9-cents-per-gallon gasoline tax is not generating the expected revenue because people are driving less. Futhermore, inflation has added about $9 million to the cost of the maintenance program alone.

Some Northern Virginia legislators have said that the state would have to have an increase in the gasoline tax and that to get it they would need Northern Virginia votes. The price of those votes, the area legislators have said, is a Metro funding package.

State Sen. Wiley Mitchell (R-Alexandria) said yesterday that "anytime Richmond . . . indicates movement in the direction of helping to finance Metro, I think it's cause for celebration."

State Sen. Adelard Brault (D-Fairfax) said he was interested in the idea, but said "I just don't believe the localities would agree "to the lack of operating aid.

The state highway commission yesterday instructed that a letter outlining the idea be prepared for Dalton on action that would make the idea a commission position. Walters himself said he was seeking reaction from both the commission and Northern Virginia.

The most commonly discussed tax increase proposal for transportation purpose is a 4 percent sales tax on the wholesale price of gasoline. That would raise sufficient revenue to cover the highway needs as well as the transit programs in Northern Virginia and eleswhere in the state, according to state estimates.