The Maryland governor's race began unofficially here last night at an elegant, $125-a-head bash, with Gov. Harry Hughes nowhere to be found.

Instead, the man of the hour was William Donald Schaefer, the mayor of Baltimore, whose political clout and recently amplified gripes about Hughes have made him the wild card in the 1982 gubernatorial election.

"This definitely has political implications," observed Attorney General Stephen H. Sachs, scanning the crowd of 2,700 that filled the cavernous convention center for what was billed as a "nonpolitical" tribute to the popular three-term mayor.

"But," Sachs added, "nobody knows what it implies."

Hughes' critics hope it implies a Schaefer race for governor, which would be sure to steal away votes and campaign dollars that Hughes drew from his populous, intensely Democratic city in 1978. With the estimated $250,000 netted from ticket sales and contributions last night, Schaefer now has a formidable campaign war schest, if he chooses to use it.

On the surface, the 59-year-old mayor is at least toying with the idea. For example, when longtime city Councilman Dominic Mimi DiPietro confronted him last night with the loud greeting, "Hello, Governor!" Schaefer leaned forward and replied: "Shhh. Not so loud!"

But many of Schaefer's close aides and financial backers insist that Baltimore's bachelor-mayor has become irrevocably wed to the city and will not leave it behind for the cloistered realm of the governor's mansion. Furthermore, the business leaders who raised the money for last night's gala, marking Schaefer's 25th year in public office, say they have a large stake in keeping him here.

"What we are saying is, 'We love you as mayor and we want you to stay as mayor,'" said Henry Rosenberg, board chairman and chief executive officer of Crown Central Petroleum. "This is his life. Otherwise he'd be like a fish out of water."

Rosenberg, a cochairman of the event, was also a fund-raiser for Hughes in 1978 and says he has no current plans to desert the governor in 1982.

Why, then, would Schaefer need $250,000 simply to seek reelection as mayor, an office he won for the third time in 1979 by a staggering 5-to-1 margin?

"Oh, I think he's tweaking the governor's nose," said state Sen. Harry McGuirk, leader of one of the most powerful political organizations in town, who is himself testing the waters for a possible gubernatorial bid.

The mayor, according to McGuirk and others, is trying to use the threat of his candidacy to "persuade" Hughes to increase state aid to the city. This is especially crucial now, as the Reagan administration prepares to ax many federal programs that helped finance Baltimore's much publicized downtown revival.

Schaefer recently has stepped up the pressure on Hughes by publicly criticizing him for "insensitivity" to the problems of Baltimore, a charge that Hughes' aides dismiss as "pure nonsense."

Still, recent polls show that the governor's approval rating has slipped, making him more vulnerable to a challenge -- if not from Schaefer or other Democrats, then possibly from his most outspoken Republican critic, Anne Arundel County Executive Robert Pascal. And Schaefer, a friend of Pascal, has hinted that he might remain silent in the event of a Hughes-Pascal race.

The ensure victory against Pascal, Hughes would probably need to follow the same strategy that saved Maryland for Jimmy Carter in November: a solid triumph in populous Baltimore. In that scenario, Schaefer is virtually indispensible because he is well known to have a hammerlock on city politics.

The mayor's prowess was especially evident at the convention center last night where the crowd that drank, danced and ate under pink spotlights included both Republicans and Democrats, business leaders and clerical workers and politcal bosses from around the city and the state.

The Schaefer fans at last night's gathering gave mostly the same reason for supporting the mayor: "He delivers," they said. The businessmen pointed with special pride to the glistening, new waterfront buildings around the convention center, many of which the Schaefer administration generously helped finance through bonds or federal assistance. Others cited weedy lots Schaefer intervened to have moved, abandoned vehicles he personally had towed away.

The praise was still coming this morning at the annual mayor's prayer breakfast, attended by more than 3,700 people, where evangelist Billy Graham was the featured speaker. Graham, who is here for a weeklong crusade, opened his sermon by paying homage to the mayor's might.

"My goodness! I've never been to a city where there's so much said about the mayor," the evangelist said. "I havenht heard one single word of criticism about him. I'd hate to run against him."