It was a party for Harry Hughes but Marion Barry wanted to do some business.

So, as Washington's mayor, who celebrated his own inaugural festivities 16 days ago, passed through the receiving line for Maryland's governor, inaugurated today for a second term, he pulled Hughes aside for some conspiratorial whispers.

"Like to have your help on the national convention," Barry said, referring to the 1984 Democratic National Convention that he wants to bring to the city's new Convention Center. "It's the kind of thing that would be good for the whole region," he said, over the music of a string quartet.

Hughes, who had changed from the suit he wore during inauguration ceremonies this afternoon to a tuxedo, smiled politely and sipped his customary Jack Daniel's and water. "Give me a call," he said, and Barry, one of the few people in Baltimore's glittering 3-year-old convention center tonight who hedged on whether he paid the $125 ticket price, smiled with satisfaction. Barry's mission for the evening had been accomplished, and he and his wife, Effi, headed for their seats at one of the head tables.

The goal for Hughes and the people who put together the inaugural dinner and ball tonight was to try to recoup an $86,000 campaign debt, left over from Hughes' landslide reelection campaign. That was the reason for the steep asking price for the dinner.

For most of the guests, this was a night to have fun over cocktails, a dinner and a ball, complete with big band music and dancing.

Only the hors d'oeuvres--carrots, celery and cauliflower with a vegetable dip--drew negative comments. "Where I come from, you get hot hors d'oeuvres," State Senate President Melvin A. Steinberg quipped. "Of course, no party like this is worth the price. We're here to pay the debt." And, he added quickly, "We're all glad to do it."

But at any political gathering, business, not the food, will be the main staple.

As state Attorney General Stephen H. Sachs, the early-line favorite to succeed Hughes in four years, went to take his seat, he was collared by real-estate magnate and Democratic fund-raiser Nathan Landow of Montgomery County.

Landow, who held several high-priced fund-raisers for Hughes, is already hard at work for former vice president Walter F. Mondale in next year's presidential race. "Here, I got something for you," Landow said to Sachs, pressing a watch with Mondale's picture and M-O-N-D-A-L-E around the dial where the numbers would otherwise be.

"Great, great," said Sachs, already committed to Mondale. "I'll always take a Fritz Mondale watch." With that, Sachs sat down, along with Barry, Steinberg and former U.S. senator Joseph D. Tydings, now head of the University of Maryland's board of regents, to a meal that consisted of Maryland crab soup, New York strip steak, California burgundy wine and, for dessert, a mocha torte. All of this to be topped just four hours later by a midnight breakfast.

Landow also said he hoped to get fellow Democrat Hughes, who has characteristically remained firmly noncommittal on the subject of next year's national elections, into the Mondale camp before a scheduled March 23 appearance by Mondale in Annapolis.

All the guests spent much of the early part of the evening waiting in line to greet Hughes and his wife Patricia, who wore a salmon-and-gold embroidered shirt and a matching long brocade skirt.

Asked if she had the dress especially made for the occasion, Patricia Hughes answered pointedly, "I had it made."

As Hughes, his wife, new Lt. Gov. J. Joseph Curran Jr. and his wife, Barbara, greeted their guests--about 1,000 for the dinner and another 700 for the ball--one of Hughes' opponents in the Democratic primary stood a few feet away, shaking every hand available.

"He can't run again and I can," said former state senator Harry J. McGuirk. "The ticket price is worth it because of all the people I can say hello to before the night is over."

Others had different reasons for paying their way. Former Prince George's County executive Winfield M. Kelly Jr., who is now working in cable TV and wouldn't mind being appointed secretary of state by Hughes, bought several seats.

"Are there freebies? I bought a whole table," Kelly said.

Several of the top lobbyists in the state attended, looking at the evening as another chance to shake a few hands and twist a few political arms.

"Am I going to have you with me on that movie censor bill?" asked lobbyist George N. Manis, who works for the movie industry, shaking hands with state Sen. Thomas V. Mike Miller.

The evening's surprise guest was the Maryland House of Delegates Republican minority leader, Robert R. Neall, who, at least in name, is the leader of the loyal opposition.

"I'm here because I got an invitation," Neall said, as one person after another asked him why he came. "Why don't you ask some other people why they're here? Anyway, everyone knows I like a good party."

The person who apparently liked the party the most was Hughes, who beamed through most of the evening and seemed almost ebullient--in sharp contrast to his normally reserved style.

"It's really been a fun day," Hughes said. "Seeing all these different people come through the receiving line makes me feel very, very good."

Knowing their presence will wipe out his debt undoubtedly made him feel even better.