A proposed gasoline tax for Northern Virginia and a requirement that hundreds of state officials file conflict-of-interest statements - issues that only last year sparked bitter controversy in the Virginia General Assembly - today whizzed through the State Senate without debate or opposition.

Supporters of the two measures, who expected a floor fight on them, said later they were astonished by the action.

The gasoline tax measure which allows five Northern Virginia localities to individually place a 4 per cent tax on gasoline sales to help meet the region's mounting Metro costs, passed by a 30-to-0 vote. The four senators who hand voted against the measure in committee didn't voye against it on the floor; they abstained.

The conflict measure, supported by Common Cause of Virginia, a citizens lobbying group, passed unanimously - an act that left its sponsor, Sen. Joseph V. Gartlan (D-Fairfax), speechless. "I don't know" why opposition to the measure vanished, he said later.

Debates on the two measures were expected to occupy much of the Senate's time today, the final day of the current session, under the Senate's own rules, in which it could act on legislation filed by members of the Senate. During the remainder of the current session, scheduled to end March 4, the Senate will have to deal with House measures.

The House of Delegates today rebuffed several attempts to provide a pay increase for state employees and passed a general appropriations bill, 93 to 0, that balances the biennial 1976-78 state budget without a tax increase.

The bill inculdes a $10 million contribution from a state mass transit fund for Metrorail construction aid. Gov. Mills E. Godwin vetoed in identical Metro aid provision in the two-year budget adopted by the Assembly last year.

The amendments to the budget adopted today avoided what many of the 100 House members feared might be a necessity when they convened on Jan. 12 - an election-year tax increase.

The two-year budget adopted last year overestimated state revenues by $220 million, according to updated estimates. The revenue gap was reduced to $102 million by the time the Assembly convened through a combination of cuts by Godwin and extension of federal revenue sharing not counted on when the state budget was adopted.

The bill passed by the House trims state spending by another $26.5 million and authorizes a loan of $35 million and maintenance trust fund to the general fund. The trust fund is financed by gasoline taxes.

The budget bill left a $40-million gap that will be closed by a speedup in collections of sales and income taxes. Acceleration of these tax collections was approved by the House yesterday and is expected to provide a one-time bulge in revenues of $40 million next year.

The Senate spent most of its four-hour session today debating a bill to create a private consumer fund to fight utility rate increases and a move supported by self-proclaimed "country boys" to divert $38.9 million in highway construction funds from cities to the state's secondary road system. The consumer fund measure passed, 24 to 13, but the highway diversion bill failed by a 16-to-21 vote.

The gasoline tax measure, which would raise between $11 million and $12 million, depending on how many jurisdictions approve it, is a revision of a similar bill enacted last year. That legislation required the approval of Arlington and Fairfax counties and Alexandria, Fairfax City and Falls Church before the tax could be imposed.

Fairfax City officials, claiming their city didn't need the tax revenues, killed last year's proposal by voting against the tax. The measure that passed the Senate today does not require approval of all five localities before it can become effective, starting next July 1, in individual jurisdictions.

Sen. William F. Parkerson (D-Henrico) threw his hands on his head and exclaimed, "Oh, my heavens!" when he realized that the gasoline measure had been quickly passed without a word of debate. Parkerson, who had opposed the measure last year, said later that the bill had "slipped by me."

He and other opponents of the tax measure said earlier they were reluctant to attempt to tell one region of the state how they should finance "that mess," a reference to the Metro subway system.

Northern Virginia senators said later they believed one reason the gas tax measure passed so easily was that the Metro opponents would use the passage of the gas tax as an excuse to kill a $10-million appropriation for Metrorail construction approved by the House of Delegates today.

Supporters of both the gas tax and the conflicts-statement bill were optimistic for House passage of their bills. Gartlan's conflicts bill would require that, in addition to members of the General Assembly, about 500 gubernatorial appointees, members of the State Corporation Commission, Industrial Commission and the Judicial Inquiry and Review Commission, as well as an undetermined number of state administrative personnel, file a brief statement on their economic holdings.

The bill directs the secretaries in the state cabinet to designate officials who deal in contracts and financial matters to file the financial statements. Gartlan said he had eliminated much opposition to the bill by removing a proposal that would have called on all state judges to make a similar filing.

Prospects for the consumer fund bill in the House are "shaky," Sen. Clive L. DuVal II (D-Fairfax) conceded today after Senate passage of his bill. It had been opposed by lobbyists for the state's major electric utilities and DuVal told the Senate he feared the lobbyists had decided, "let's get them on the other side," the House.

DuVal's bill is substantially weaker than the initial measure he introduced a year ago which would have required utilities to bill their customers for a special fund to be used by consumer groups in fighting rate increase applications. Under the bill passed by the Senate, the utilities would be required only to insert statements in their bills asking for voluntary donations to the "Virginia Residential Utility Consumer Foundation," a group to be governed by a board named by the governor.

As expected, the House gave final approval, today, 82 to 12, to a death penalty measure that is intended to bring the state's capital punishment law into line with recent Supreme Court rulings.

The bill, which provides for a two-tiered jury system where verdicts and sentence would be determined in separate proceedings, would make the death penalty mandatory for any of five types of murder. These include murder fo a prison guard by an inmate, murder for hire, murder of a kidnaping victim held for ransom, and murder commited in connection with a rape or robbery.

The bill will now go to the Senate where easy passage is expected.