Troubled but undaunted by the opposition of Virginia Gov. John N. Dalton and some key legislators, most Northern Virginia members of the General Assembly vowed today to work for passage of a special Metro sales tax in the Washington suburbs.

Their commitment, reached at a morning caucus, appeared, however, to come more out of a sense of obligation than a hope for victory.

Speaking to Sen. Omer L. Hirst, chief patron of the tax bill, Del. Martin L. Perper (R-Fairfax) said, "To let this bill stay in your desk drawer would be an abdication of what we were sent down here to do this year.

"I think the governor should have this bill put on his desk and be required to make up his mind publicly," Perper declared.

Hirst led a delegation of three senators to the governor's office last woeek the day after Dalton delivered his legislative message, but failed to change the governor's mind. "He told us, 'I never say in advance that I will veto any bill, but I will have to change my mind on this one before I sign it,'" Hirst sadi.

Senate Majority Leader Adelard L. Brault (D-Fairfax) urged the Northern Virginia legislators to press for action early in the session. Passage of the bill more than seven days before the session's end would enable the Northern Virginians to try for an override of a veto.

However, they appear to have little chance of getting the necessary twothirds vote to override a veto in the House, where the measure is opposed by three influential Democratic leaders -- Speaker John Warren Cooke (Mathews), Majority Leader A. L. Philpott (Henry) and Finance Committee Chairman Archibald A. Campbell (Wytheville).

Yesterday, Sens. Wiley F. Mitchell (R-Alexandria) and Edward M. Holland (D-Arlington), who took part in the meeting with Dalton, said they think the effort to pass the bill should be made.

"I am optimistic that we will be able to persuade the governor that the view he expressed is incorrect," Mitchell said.

Although not all 23 legislators from cities and counties served by Metro were present at yesterday's caucus, it appears that all but two will either cosponsor or vote for the sales tax bill.

Two Republican delegates from Fairfax, Robert L. Thoburn and Robert E. Harris, voted against the bill last year and still oppose it.

After relatively easy passage in the Senate last year, the proposed 1-cent increase in the current 4-cent sales tax failed by a single vote to win the necesssary 51-vote majority in the House of Delegates.

The bill that Hirst is expected to introduce Tuesday or Wednesday is loaded with most of the provisions added in the House last year to make it more palatable to opponents.

To become effective under this proposal, voters in all three cities and both counties served by Metro would have to approve imposition of the tax in their localities before it could become effective in any of them. Thereafter, voters could repeal the tax in their city or county without affecting it elsewhere.

Up to two-thirds of the $40 million the tax would be expected to produce annually could be applied to Metro operating deficits. However, any city or county using the money for Metro would have to reduce its other taxes by an equal amount.

John W. Purdy, chairman of the Northern Virginia Transportation Commissionn (NVTC) and a member of the Arlington County Board, urged the delegation to require a rollback in other taxes equal to the entire sales tax collection. He said this should make the bill easier to pass and more likely to get Dalton's approval.

Hirst disagreed and said he would like Fairfax to get additional sales tax revenue without having to reduce other taxes. Fairfax would get an estimated $12 million in addition to the amount needed for Metro deficits and could use the money for other transportation purposes.

Arlington would have no money left over after its Metro deficit was paid, according to NVTC estimates, and the three cities of Alexandria, Fairfax and Falls Church would have relatively small amounts left after deficit payments.

The proposed tax would expire after five years under terms of the drafted bill and would automatically be repealed by passage of a state-wide increase in the sales tax.

Some members of the delegation have expressed fears over running for reelection in the same year that the tax referendum is on the ballot, but it appears likely that the referendum provision will remain in the bill to help its chances of passage.