It was touted as the main event in Maryland's Democratic gubernatorial primary, the only debate between Gov. Harry Hughes and his two Democratic challengers. But the live television event proved to be as sleepy as the rest of the campaign.

The highlights of the debate sponsored by WMAR-TV Channel 2 included a proposal by Ocean City Mayor Harry Kelley to build a monorail transit system throughout Maryland, a statement by Baltimore state Sen. Harry McGuirk in support of the death penalty for those involved in the "manufacture of illegal drugs" and a refusal by Hughes to rebut one question because he simply had nothing more to say on the issue.

"I'm trying to learn that I don't have to respond directly to the questions," said Hughes at the end of the one-hour event, which, like the primary campaign, was marked by few sharp differences on issues. "There's no winners. How can there be winners with six questions."

McGuirk and Kelley had been hoping the debate would give them an opportunity to gain on Hughes by highlighting differences between the candidates or prompting the governor to blunder.

But none of that happened as the three men proceeded mildly through questions on mass transit, prisons, the death penalty, abortion, the role of the lieutenant governor and the impact of federal budget cuts on Maryland.

Each candidate returned to standard campaign themes. Kelley emphasized that he was tough on crime, saying "it was safer to be in World War II than to walk the streets of cities today."

McGuirk decried what he called the lack of aggressive leadership by the incumbent. And Hughes focused on the issue his polls indicate the voters respond to -- integrity in government and a scandal-free administration.

McGuirk began the debate aggressively, turning to Hughes to accuse him of allowing the state's unemployment and crime problems to fester and permitting Maryland's economic decline.

"Your governor has chosen to ignore these issues," he said. "But governor, you cannot ignore the fact that we have the highest unemployment ever. . . that six of every seven offenders receive probation or that we have 10 escapes per week during your administration."

From that point on there were no sharp exchanges and some points on which they all acknowledged seeming agreement.

On the issue of prison policies the three candidates agreed on the need for more prison space. McGuirk said Hughes had been too slow in moving ahead on prison construction, to which Hughes responded that his administration had launched the largest prison construction program of any administration.

When asked how they would deal with future federal budget cuts, including which programs they would be willing to eliminate and which they would never sacrifice, the three avoided specifics, saying only that Reagan administration cuts were the most difficult issue facing state government.

They all emphasized the need to bring new business and more jobs into the state.

Kelley and McGuirk then came out strongly for capital punishment, with Kelley saying, "I'd like to see us institute the death penalty immediately if not sooner."

McGuirk repeated his suggestion that those convicted of manufacturing heroin be given the death penalty.

Hughes carefully avoided stating his personal views on the death penalty (he opposes it), saying only that as governor he would examine each case brought before him individually before deciding whether to commute a death sentence.

Asked later why he had not mentioned his personal views before the television audience, Hughes, whose polls show that opposition to the death penalty is unpopular with voters, said only, "I forgot."

Kelley and McGuirk said they were personally opposed to abortion on demand but would not tamper with the current system of state funding of Medicaid abortions. "I would not fund for a casual affair or a rendezvous," said McGuirk.

Hughes said he was prochoice. "Poor women should have the same rights to abortion as women of means," he said.

Surprisingly, McGuirk failed to criticize Hughes on the issue of the role of the lieutenant governor when asked about the issue. McGuirk chose as his running mate Lt. Gov. Samuel W. Bogley whom Hughes dumped after a bitter four-year partnership.

All the candidates expressed their support for the subways in suburban Washington and Baltimore, and said they saw no need for a regional tax to compensate for future federal cutbacks in operating funds for mass transit.

At the conclusion of the debate, McGuirk, who has been lagging in polls and suffering from a lack of money that would allow him more media exposure, called for another debate. Later, he said, the debate "is important, it gives me exposure. I would hope other stations would pick it up."

The evening was summed up by Hughes' campaign manager, Joseph M. Coale III, who took a quick glance at the audience as the final comment was made and quipped, "Everybody still awake?"