The Maryland General Assembly tonight killed Gov. Harry Hughes' proposed gasoline tax increase as well as his plan to recognize the state racing industry in a marathon final session dominated by filibusters and confusion.

The proposed 1-cent-per-gallon increase in gasoline taxes was voted down by the House Ways and Means Committee after a long day of behind-the-scenes negotiations failed to satisfy the demands of House leaders that the bill be amended and that they receive assurances that the Senate would pass the amendments.

The racing bill, the subject of constant redrafting and political manipulation over the last two months, died only an hour before the end of the session when a move to cut off debate failed for the second time.

The racing measure, which called for the creation of state authority to negotiate a buy-out of the Bowie thoroughbred track for up to $12 million, was ordered to the back of the Senate's clogged agenda this afternoon after Senate leaders were unable to muster the votes to stop a filibuster by Prince George's County Sen. Thomas P. O'Reilly.

The two major losses on the last day of an already disappointing session left Hughes and his aides despondent and somewhat bitter tonight. "We have nothing but regrets," said Ejner J. Johnson, the governor's chief of staff.

Hughes' lobbyists, who spent the final day frantically shuttling between House and Senate leaders with compromise proposals for the gasoline tax, blamed House leaders tonight for the bill's defeat. They said that they had won enough votes in the Senate to prevent a filibuster and pass the tax with the amendments favored by the House, satisfying the conditions of House Speaker Benjamin L. Cardin (D-Baltimore) for moving the bill.

Cardin and other House leaders disputed the governor's head count, however, saying that their own tally convinced them that the bill would be filibustered or voted down by the Senate even if they managed to push it through the House before adjournment. "It was just a matter of time," Cardin said. "Hours made the difference."

The final dispute over the gasoline tax was typical of a day that saw bitter disputes over a dozen eleventh-hour issues and a proliferation of filibusters in the Senate that forced the death by time of many other measures.

The only major legislation to get through the assembly by late tonight was a $13 million education aid package that will grant additional funds to the state's community colleges and give $8 million in "targeted" aid to needy school districts. This education package, the first priority of Cardin and Baltimore City officials, was the only piece of Hughes' $68 million tax and spending package to be enacted by the legislature.

Senate Majority Leader Rosalie Abrams (D-Baltimore) denounced what she called the "tyranny of the minority" in the Senate, where the racing plan and four other controversial bills had been delayed -- and thus probably killed -- by filibusters the leadership was unable to stop with cloture votes.

Dozens of other measures, including a bill raising the state's drinking age, were blocked by the filibuster-assisted backlog in the Senate, and died for simple lack of time.

A measure raising the drinking age to 19 finally cleared the Senate at 10 p.m. but had to go back to the House, which had passed a measure raising the age to 21 but defeated 19 twice before. The bill never came to a vote.

The state's $90 million capital budget was not approved until three minutes before the midnight adjournment. If time had run out on that bill, a special session would have been necessary.

Eliminated from the budget were all funds for community rehabilitation centers for prisoners -- a move that reflected legislative unhappiness with the Hughes administration's prisons policy. According to prisons officials, 338 prisoners would be affected, and the state's already serious overcrowding problem would be exacerbated.

Only one filibuster had been halted by a cloture vote -- the one-man stand by Prince George's Sen. Tommie Broadwater against a county school board redistricting plan that he contends was not properly considered and is drawn to hold down the number of black school board members.

Prince George's Sen. Thomas V. (Mike) Miller managed to win enactment for the plan only after promising to vote for all other cloture motions and trading, he said, "my left leg."

During spurts of activity, the Senate also enacted a state subsidy for Conrail trains serving the Washington-Baltimore corridor and the last of six bills sponsored by Hughes to toughen laws governing drunken driving.

Mostly, however, the Senate occupied itself with routine bills, punctuated by filibusters and delays of controversial bills. The House, meanwhile, spent most of the final hours idly waiting for the Senate to act.