RICHMOND, MARCH 2 -- Virginia House of Delegates Speaker A.L. Philpott used his unrivaled parliamentary power today to kill a sales tax relief bill sought by Lt. Gov. L. Douglas Wilder, saying the vehicle for the tax measure was unconstitutional.

The death of Wilder's plan to exempt nonprescription drugs from the state sales tax highlighted a busy day as the General Assembly worked toward adjournment 10 days from now. In other action today:

A key state Senate committee voted 8 to 7 to allow voters in November to decide whether to permit pari-mutuel betting on horses. The House has approved the legislation, and the Senate is expected to follow suit.

The Chesapeake Bay Preservation Act, which would require water quality to be considered in zoning decisions in Tidewater Virginia and bring the state into line with Maryland in protecting the bay, passed the Senate and was sent to Gov. Gerald L. Baliles, who has pledged to sign it.

Legislation to permit private financing and construction of an extension of the Dulles Toll Road from the airport to Leesburg passed the Senate and was sent to Baliles, who has said he will sign it.

Wilder, who spent 20 minutes with Baliles before the House action on the sales tax exemption bill, said he was convinced that the governor, who opposed the measure, played no role in its defeat.

Wilder said he will "do nothing further" this year to revive the legislation, which got a second life Monday when, with the help of Senate Republicans, it was tacked onto a House-passed bill changing telephone company taxes. The Senate Finance Committee earlier had refused to bring the measure to the floor.

Philpott said combining the disparate ideas in a single bill was "plainly unconstitutional." Because of that, the sponsor of the telephone tax bill, Del. Lewis W. Parker Jr. (D-South Hill), withdrew his bill today, which also had the effect of killing Wilder's proposal.

Wilder said he did not interpret the House action as resulting from "any desire {by Philpott or others} not to see it pass because of my interest in it."

"This is not the last time we'll see this measure," Wilder said. "It obviously will pass the Senate again next year. And if it would have come up on the {House} floor for a vote, it would have passed, no question about it.

"It will pass in 1989," Wilder said. "The difference between the two bodies is timing. I felt now was the time, they felt later."

If Wilder's prediction is correct, the tax break would become law in time for Wilder to point to it in his expected campaign for governor.

The pari-mutuel betting bill squeaked out of the Senate General Laws Committee, which heard more than two hours of often-emotional appeals on both sides of the issue.

Proponents, led by Del. Raymond R. (Andy) Guest Jr. (R-Front Royal), a wealthy farmer, included horse breeders and other industry spokesmen who said racetracks would generate tens of millions of dollars for the state economy and hundreds of new jobs -- benefits, they said, that neighboring racing states have reaped at Virginia's expense.

"This is a cry for help from the industry," Guest said. "We're asking you to let the people speak on this issue."

Opponents, including a number of spokesmen for religious groups and one woman who read from the Bible to illustrate the evils of gambling, aired many of the same complaints used in last year's fight against a statewide lottery referendum. Gambling on horses, they contended, would be just as pernicious as betting on numbers; organized crime would enter the state and Virginians' "quality of life" would decline, they said.

Alexandria City Council member Carlyle C. Ring Jr., a Republican who opposes the proposed referendum, accused committee members of ducking the hard questions about betting by putting the issue on the fall election ballot. "You're in a better position to decide, rather than casting it upon the waters for the people to decide," Ring said.

The chief Senate sponsor of the latest Chesapeake Bay clean-up effort, Sen. Joseph V. Gartlan Jr. (D-Mount Vernon), said, "This is not just supported by environmentalists who hug a tree and then want a law," but is an important step toward "asserting and protecting water quality and habitat in the bay."

Del. W. Tayloe Murphy Jr. (D-Northern Neck), who introduced the proposal, called it "landmark legislation" similar to a "critical areas" legislation adopted by the Maryland legislature two years ago.

The bill creates a nine-member state board whose members will develop criteria that affected local governments must use in making zoning decisions.

Before approving the bill, 36 to 3, senators rejected two amendments that would have delayed the enactment by one year and required the legislature to approve the standards before they are imposed on the localities.

The only Northern Virginia jurisdiction whose streams are not affected by tides, and therefore is exempt from the bill, is Loudoun County.

In all other cities and counties in Northern Virginia, zoning actions taken after July 1990 must consider water quality standards, which the new board has until July 1989 to adopt.