Because Gov. Harry Hughes had a dinner party, and a delegate had to attend a funeral, and a rookie committee chairman ran away, refusing to break a tie vote, the annual legislative effort to require trucks to cover their loads on Maryland's highways failed again this year.

The end came Friday, on a 11-to-11 vote in the House Environmental Matters Committee.

But until the last moment, it appeared that after 20 years of trying, proponents might pass the controversial bill this year.

The committee normally holds its voting sessions on Thursdays, but on this most recent Thursday, it got bogged down in a long hearing schedule.

By the time that business was finished, it was almost 6:30 p.m., the appointed time for one of the several black-tie dinners the governor holds for legislators during the session at the Governor's Mansion. Several committee members, knowing the debate on truck covers would be long, wanted to delay the voting session until Friday.

One member who did not want the delay was Del. Margaret H. Murphy (D-Baltimore). Murphy had a funeral to attend Friday afternoon and she wanted to vote on the truck-cover bill. Del. Joan B. Pitkin (D-Prince George's), a supporter of the legislation, had Murphy on her list as a likely yes vote.

But the consensus of the committee was you don't keep the governor waiting, so the voting session was postponed.

Friday morning, proponents and opponents were lobbying each other. Freshman William H. Clark (R-Harford), an avowed opponent, drew pictures of trucks at his desk for Del. Robert Kramer (D-Anne Arundel), another freshman, who was undecided.

At the same time, the Senate, after a typically rancorous hour-long debate, voted 27 to 18 against a compromise no-peaking bill, which would prohibit carrying uncovered loads above the height of the side of the truck.

"Screw them," said its sponsor, Sen. Arthur Dorman (D-Prince George's), who before the vote had promised his colleagues he would not try again this term three more years for his half-a-loaf measure. "Next year, no compromise like this. I'll go for truck covers again and again until we get it done."

Word quickly spread across the marble hallway that the no-peaking bill was dead. Pitkin saw it as reason to persuade fence-sitters that her bill had to go or nothing would go at all this year. Del. Larry Young (D-Baltimore), the committee chairman, winced upon hearing the news. "It's already real close," he said. "The last thing in the world I want is a tie."

Young held the truck-cover bill until last among the 20 bills being considered Friday. When the debate began, he told his members, "I want you all to talk until you've got nothing left to say. When I leave here today, I want to be through with this one way or the other."

So they talked. The arguments were the same as ever. Freshman Del. W. Timothy Finan (D-Allegany), even though he was an opponent, said, "We were supposed to vote on this last night. Del. Murphy could not be here because we changed the vote. Is that fair? Should we hold this until next week?"

They argued about that. But without a vote, the debate simply continued. There was no motion to delay. Proponents had one last card: An amendment that would delay implementation of the bill for a year, to July 1, 1984. It was designed to take steam out of the argument that now is a bad economic time to to impose a costly requirement on truckers. It also meant that even if passed, the legislation could be killed next year before it went into effect. But, Pitkins and her allies felt it is easier to get a law on the books than off them. The amendment passed.

The debate went on. Finally, Del. Marilyn Goldwater (D-Montgomery) suggested it was time to call the question. "We all know how we're going to vote," she said, "And I have to leave for a doctor's appointment."

That ended discussion. The role was called. It was 11 to 11. Murphy's vote would have been the needed 12th vote. Young could still provide it. All eyes turned to him. He busily counted the votes.

"The vote is 11-11," he announced, "with the chairman not voting."

While committee chairmen rarely vote, they can assert their leadership by breaking tie votes. Because the House of Delegates seldom goes against the advice of its committees, a chairman who votes to send a bill to the floor is virtually assuring passage of the legislation by the 141-member body.

"I did it for committee unity," Young said. "I knew this was going to be close, and I told both sides earlier today I wouldn't vote."

So for a 20th year, the bill was dead. There is still a no-peaking bill to be considered by the House, but as Pitkin said, "I think you know what will happen to that. Of course, I never say never. You never know down here what will get a bill passed."