Republican challenger Robert A. Pascal went on the attack tonight in what may be the only televised debate of the Maryland gubernatorial contest, accusing Democratic Gov. Harry Hughes of failing to combat crime, vacillating on prison construction, and waiting until an election year to begin needed road repairs.

Urging Maryland's heavily Democratic electorate not to make voting decisions along party lines, Pascal said, "If you are happy with the way crime is on your streets, happy with economic development, with hazardous wastes, and with the health of the bay, then you have to vote for Mr. Hughes. I would like to change things."

Hughes, appearing the confident incumbent, responded cooly to many of Pascal's attacks and accused the Republican of demagoguing on the issue of hazardous waste, mistating facts or misinterpreting state law and taking a negative view of Maryland.

The hour-long debate, televised live on three Baltimore stations and to be repeated Sunday afternoon on Washington's WJLA-TV (Channel 7), produced sharp distinctions between the rivals on such issues as abortion, the business climate in the state, tuition tax credits and prayer in public schools.

Afterward, Hughes said he felt "good" about his performance. His press secretary, Lou Panos, said bluntly, "I don't think the debate changes a damn thing."

With just over three weeks remaining before the Nov. 2 election, Pascal had hoped the confrontation would move him closer to the front-running incumbent. Pascal admitted that he was nervous in the first half of the debate, but when it was over he said, "I felt good the last half. I thought I showed how sharp the differences are between myself and the governor. That's what I came here to do."

While neither candidate would declare himself a winner or loser, Pascal said he would like to "do this every morning, every day of the week." Hughes, although questioned repeatedly, would not say whether there would be another debate. "I'm not ruling it out," he said, "but I'm not going to plan my campaign schedule to accommodate my opponent."

"We've heard a lot of complaints from my opponent and I'm not going to take the time to respond to every one of them," Hughes said. "The real issue is whether you want to continue what was started four years ago when you elected me your public servant. We're building roads, we're building prisons and we're returning tax dollars because that's what you demanded."

Both men sounded familiar themes. Pascal raised the question of whether Hughes would debate him again while Hughes tried to wrap the national administration around Pascal's neck, referring to it as "the Republican administration of my opponent."

Pascal touched on the same issues he has tried to highlight throughout the campaign: crime and prisons, juvenile crime, unemployment, aid for the elderly and the death penalty. He accused Hughes of "vacillating" on prison construction, pointed out that Hughes is opposed to capital punishment whereas he favors it, and repeated a promise to establish a cabinet post to administer aid to the elderly.

Hughes, as always, emphasized the recurring theme of integrity in government, which he rode to office four years ago after two successive governors were embroiled in corruption. Hughes' polls show the issue is still important to voters.

On the Reagan administration, Hughes stared into the camera and told the voters, "Your state is solid and strong and ready for any challenge which comes from Washington." He added, "Do we want to accept the Republican political philosophy that has failed America or continue the Democratic politices which have served this state well in good times and bad?"

The first question from the panel of four reporters was on handgun laws. Pascal used it to talk about lack of prison space, pointing out that there are 8,500 beds in Maryland prisons and 11,000 prisoners. Hughes responded that the crime rate has gone down for 1 1/2 years. Pascal countered that the figures looked good now only because they had been so bad under Hughes' early prison policy, which he abandoned 18 months ago. Hughes countered that the detention center in Anne Arundel County, where Pascal is county executive, had turned prisoners away because of inadequate staffing. "That," he said, "has never happened to the state system."

Neither candidate offered a specific solution on how to deal with federal cutbacks, but each said there was no reason to increase taxes to deal with them.

On unemployment, Pascal criticized the business climate in the state, pointing to a "D" rating the state was given by a business magazine. Hughes replied that a more recent issue of the magazine raised Maryland to a "B."

They differed on tuition tax credits for parents who send children to private schools. Hughes said he was absolutely opposed to it while Pascal said it should be considered.

Pascal's answer reflected a slight backing off from his past position, when he indicated he would support legislation granting such credits to parents who send their children to parochial and other private schools.

On another school issue, Pascal said he "had no problem" with organized voluntary prayer in public schools, if the local school board approved it. "We shouldn't get so extricated about it," he said. "It's not the end of the world and who knows, it might do some good." Hughes said he was opposed to organized voluntary prayer.

On abortion, Pascal hedged, saying he favored allowing women to have abortions for health reasons or in the case of rape and incest, as current state law for medicaid-funded abortion permits. But he did not mention another phrase in the state law that permits abortion for mental health reasons. If that language were eliminated, the number of legal abortions would be sharply curtailed. Hughes included the phrase and said abortion should be a choice of the pregnant woman in consultation with her doctor.

The debate, sponsored by the University of Maryland law school alumni, the League of Women Voters and the United Way, climaxed weeks of maneuvering by the Pascal and Hughes camps.

Originally planned as three events run separately by each organization, the merged debate came about at the insistence of the Hughes campaign, which maintained that the governor's schedule was too crowded to fit in three televised debates.

The Hughes camp apparently has fixed it so that today's debate will be the only televised joint appearance of the campaign, a point of frustration for Pascal, who believes he needs to increase his state-wide visibility and name recognition to have a shot at unseating Hughes on Nov. 2.

Pascal has only recently raised enough money to air television advertisements. A joint debate, according to his campaign staff, ensures wide television coverage.

Hughes, on the other hand, has enough money and name recognition after nearly four years as governor. Polls show that nearly all voters know who he is as compared to Pascal who is known by just over 40 percent.