Legislation that would have allowed Northern Virginia localities to impose a one cent sales tax for Metro operations in the Washington suburbs died today by a 10-to-8 vote in a legislative committee.

Defeat of the bill in the House of Delegates Finance Committee was a major loss for Northern Virginia legislators. They have tried for two years to win approval of a sales tax increase that would help the suburbs meet their increasing Metro costs and end their dependence on local property taxes to finance the bus and rail system.

The tax bill passed the Senate, 30 to 10, earlier this session but was considered to be in trouble in the House, where it was opposed by powerful Democratic leaders. Republican Gov. John N. Dalton also had all but promised to veto the bill if the Assembly approved it. He said he is opposed to any regional taxes in the state.

"We will just have to come back and ask for it or something like it again next year," Sen. Edward M. Holland (D-Arlington) said after the committee vote. "The General Assembly committed itself to Metro 21 years ago and it is a commitment that it will have to face up to someday."

The committee that defeated the Metro tax today last year reported a similar measure to the 100-member House, where it received a 50-48 vote of approval. That was one vote short of the absolute majority needed to authorize a new tax.

Although supporters of the tax bill were fearful of Finance Committee rejection, they were disappointed by the margin of defeat. The metro tax opponents were absent when the vote was taken, so the actual lineup in the committee was 12-8 against the bill.

Del. Ray L. Garland (R-Roanoke), who voted for he measure last year, opposed it today and Del. C. Richard Cranwell (D-Roanoke County) voted against it despite Northern Virginians' hopes that he might support the bill.

Garland said he voted no because he does not like substitution of a sales tax for property taxes. The bill would have required the localities to make a dollar-for-dollar reduction in property taxes to offset the sales tax increase.

"This bill was based on the premise that a sales tax is less regressive than the property tax," Garland said. "That just isn't so. The propertied class loves a sales tax. One of the great flaws in the proposal was that it would mean a bonanza for landlords who would get a property tax reducion that they certainly would not have passed on to tenants."

Sales taxes are generally regarded as regressive, which means that lower income taxpayers pay a larger share of their income in sales levies than do higher income taxpayers. The property tax often is labeled regressive, but a recent state study concluded that it probably falls more heavily on upper income taxpayers.

Despite the opposition of Dalton, three of the five Republicans on the committee voted for the bill.

Del. Warren G. Stanbaugh (D-Arlington), who mananged the bill in the House, said that recent votes on a proposed constitutional amendment to limit state taxes may have played a role in the defeat of the Metro tax.

Stambaugh said at least one Finance Committee member was piqued by a motion Monday by Del. Martin H. Perper (R-Fairfax) to reconsider a Finance Committee vote defeating the proposed constitutional limit. This forced another recorded roll call on the sensitive issue in an Assembly election year, leaving some committee members miffed at Perper, a Metro tax supporter.

Although the sales tax increase would not have resulted in a net revenue gain for the Northern Virginia localities served Metro, it was sought to establish a fund guaranteeing payment of transit operating deficits. U.S. Secretary of Transportation Brock Adams has told Metro officials that the federal government, in allocating transit grants, will favor localities that have earmarked funds for transit operations.

In 1977, the Assembly approved a gasoline sales tax for Northern Virginia for Metro operations, but this proposal died when the Fairfax City Council refused to give its required approval of the regional tax.

Also today, the House Courts of Justice Committee killed Senate-approved legislation that would have had the effect of exempting certain county prosecutors from the requirement that they hold their posts on a full-time basis in 1980. The Assembly passed legislation in 1977 that requires commonwealth's attorneys in counties with more than 35,000 residents to become full-time prosecutors that year.

Sen. Charles J. Colgan (D-Prince William) had sponsored a bill on behalf of Prince William prosecutor Paul Ebert and nine other part-time prosecutors that would have allowed them to continue their jobs on a part- time basis if voters in their localities approve.

Colgan argued that prosecutors with more than 10 years' experience should be allowed to retain their outside law practices, such as Ebert now has, if they are reelected to their posts on that basis.

But House committee members opposed making any exceptions, saying the intent of the 1977 legislation was to phase out such outside activities by county prosecutors and avoid potential conflicts of interests.