On the opening day of the Maryland General Assembly, a half-dozen state senators rose from their desks to offer glowing tributes to their leader, Senate President Steny H. Hoyer (D-Prince George's).

The speakers were carefully picked by Hoyer, not just to represent varying Maryland regions and constituencies - rural, inner city, women - but to reflect the esteem of senators who had not originally supported Hoyer for the Senate presidency, people who "now perceive me as having done an excellent job," in Hoyer's words.

Hoyer is running for governor in a race that doesn't officially start for over a year. But the care with which he orchestrated the opening day ceremony underlined his awareness that statewide campaigns can be won or lost long before the aspirants file their candidacies.

Hoyer's effort is early, precise and methodical, geared toward building credibility - a show of force that will impress his opponents and the people who finance million-dollar political campaigns. His first fund-raiser will follow in March. It, too, is early.

Such activity creates "the appearance that he's a real candidate," said State Sen. Melvin Steinberg, (D-Baltimore County), explaining why he has publicy endorsed Hoyer for governor so early.

In the eyes of most Annapolis observers, Hoyer's campaign went public during last year's legislative session. While most Senate presidents have assumed a leadership role in championing one or two legislative causes, Hoyer offered something for everyone.

He drafted and shepherded to law sweeping changes in the state's rape laws long urged by women's organizations. He successfully sought a bill - lobbied by Jewish organizations - to outlaw participation in Arab-inspired boycotts by Maryland businesses. Common Cause and other "reform" organizations won his backing for an open meetings bill and creation of a statewide special prosecutor to fight political curruption. Hoyer championed several important pieces of environmental legislation as well.

Hoyer's schedule (he was at the polls in Baltimore on election day) is already that of a campaigner: there are appearances in Hagerstown, College Park, Adelphi, Beltsville, Baltimore, Bethesda, Bowie and Laurel - all in the opening weeks of the General Assembly.

Hoyer said his "first strategy" is to become a credible candidate. He concedes that in most areas of the state, people don't know who he is. Becoming credible does not mean, for Hoyer, just attracting publicity. He is trying to line up the support of local politicians and community leaders as well.

If Hoyer makes a good impression, their opinions of him "will filter back into the community," said Peter F.O'Malley, Hoyer's calose friend, chief political strategist and leader of Prince George's County's powerful Democratic organization

The appearance of activity is often as important as the activity itself at this stage. In the last two gubernatorial elections, Maryland Gov. Marvin Mandel frightened away potential Democratic challengers by raising enough money and obvious support months before the campaign to make it appear doubtful that anyone else could compete.

Hoyer's potential opposition - including Lt. Gov. Blair Lee III. Comptroller Louis L.Goldstein, Attorney general Francis B.Burch, Baltimore Mayor William Donald Schaefer. Baltimore County Executive Ted Venetoulis - is formidable. Schaefer and Burch have strong supporters among the powerful network of political organizations that runs Baltimore politics and got Mandel elected.

While Hoyer is no position to preempt the field now, his flurry of activity may help protect him from being preempted early by any of the others.

Commitments and endorsements inevitably do not come for nothing. Asked if any "invisible chits" or promises has been made in exchange for help. O'Malley responded: "I think it would be naive to assume that an invisible chit isn't out there" with an "indeterminate" value.

"Our approach ahs always been to run our business as a business," said O'Malley, of teh business of politics. He is general manager of the Washington Capitals, attorney for the Capital Center and a member of the state Board of Regents. "If you don't discipline yourself and set up a sensible program, your emotions get out of hand and you start reacting," he said.

Hoyer and O'Malley are both aware that such early vigor can also be a liability. In early 1974, O'Malley (using similar strategies) helped put together the slate of candidates that now controls every state and local elective office in Prince George's County.

"If we were going to go back and do it again," said O'Malley, "maybe we ought to be a little less efficient. Those things that are seen in business and sports as positive qualities are for some reason seen in politics as negatives - organization, preparation, readiness . . ."

And Hoyer has been privately criticized by some of his colleagues for being in too much of a hurry. He will be 39 years old in 1979, when he or someone else will be sworn in as governor.

"There was never a time I was not accused of being too young." He said. When he announced that he would seek the State Senate Sen. Roy Staten (D-Baltimore county), who also wanted the job, told Hoyer, he had "lots of time" and should wait. Hoyer recalls that his response was, "Yeah, but I have 14 votes to your 2. Why should I wait?"