For almost a year, Baltimore Mayor William Donald Schaefer has been telling people across the state -- except reporters -- that he intends to run for the Democratic nomination for governor this fall. In recent days, Schaefer has even taken to wearing a "Vote for me!" button, which is pinned inside the lapel of his suit and uncovered in suitable company.

But the mayor's political aides, who work out of a full-fledged campaign headquarters in Baltimore, insist that Schaefer still needs to be convinced that he should run.

So last night they choreographed what Schaefer campaign manager Mark Wasserman termed the "culminating event" in a "grass-roots effort to create a statewide demonstration of support" for a Schaefer candidacy.

According to Wasserman, thousands of Maryland voters gathered at more than 600 locations across the state to collectively urge the mayor to abandon the office he has held for 14 years and run for the State House in the Sept. 9 Democratic primary. Schaefer visited several of the parties.

At 7:55 p.m., people at the parties watched a five-minute film tribute to Schaefer, 64, and his years as mayor of Maryland's largest city, broadcast on independent stations in Washington, Hagerstown, Salisbury and Baltimore. And although Schaefer made no firm declaration of his candidacy, supporters hoped that the events would give the mayor an instant organization as the partygoers were urged to sign on as volunteers. The parties also were intended to help establish the mayor as a statewide, rather than Baltimore, figure.

At several parties he attended in Prince George's and Montgomery counties and in the Baltimore area, Schaefer left little doubt of his intentions.

Speaking at one gathering of about 50 people in North Bethesda, he said, "Am I going to announce anything tonight? Not formally, but you get a pretty good idea . . . . When, if, whatever the word, I announce for governor, I will do it because I am the most qualified person."

A preview of the Schaefer candidacy also came in the five-minute film shown last night. It offered panoramic views of Baltimore, highlighting its renaissance, and tributes to Schaefer from public officials and citizens from around the state, including two legislators who are considered possible running-mates. It portrayed Schaefer as an effective leader who "even calls on the president of the United States to get things done," showing a picture of the mayor meeting with President Reagan in the Oval Office to bring the point home.

The film's message, that Schaefer's "intensely human style of leadership" would be transferred to Annapolis for the benefit of the entire state, was echoed by some of those attending last night's events.

"I think he'll do the same for the state as he's done for the city," said Lance Berkowitz, a Reisterstown pharmacist whose Baltimore County home Schaefer visited to watch the film. "He's a go-getter."

In Reisterstown, Schaefer also criticized his opponent for the Democratic gubernatorial nomination, state Attorney General Stephen H. Sachs, without naming him, for failing to prevent the state's savings and loan crisis, and for proposing a 1-cent increase in the sales tax to aid education programs.

Wasserman, who left a City Hall job two months ago to begin organizing the mayor's gubernatorial effort, solemnly predicted that last night's house parties would "have a substantial effect" on the mayor's decision. "It's a true opportunity for not only people around the state, but for the mayor to get a first-hand feel for the kind of strong, genuine and sincere feeling about his making the move from mayor to governor."

Responded Blair Lee IV, Sachs' campaign manager: "The suspense is killing me."

If Lee and Sachs doubted the contention that the mayor is awaiting a "draft Schaefer" movement to coalesce before joining the race, they nonetheless welcomed an event that propels Schaefer a full step closer to an open campaign in which they can confront him on the issues.

"I congratulate the mayor on his political birthday," said Sachs. "What I hope today will mark, finally, is his acknowledgment of what all the rest of us know, that he is a candidate for governor, and that he begins to address the issues that the next governor of Maryland has to face. The people of Maryland want an election, not a coronation. If tonight is the last step in that journey to a campaign, I'm all for it. Hallelujah."

In recent months, Sachs has been frustrated by his inability to entice the mayor into debating such issues as gun control, education aid and their respective philosophies of governance. Schaefer, in what many observers said was a tactical maneuver designed to protect his commanding lead in the polls, has coyly avoided the fray, insisting he is too busy managing the affairs of his city to engage in a protracted gubernatorial campaign.

Last night's demonstration of support for Schaefer was officially organized by Marylanders for Schaefer, an ad hoc organization founded by former Laurel mayor Robert DiPietro. In recent weeks, however, the organization of the parties has shifted to the mayor's campaign committee known as "Reflections."

The mayor himself, during a trip to Frederick two weeks ago, spent part of his day meeting with local organizers of last night's parties, a meeting from which the press was barred. That was only the latest overt sign that Schaefer is taking a more active role in his own campaign than is officially acknowledged.

As early as last June, Schaefer told delegates to a Maryland Association of Counties convention in Ocean City that there was "no question" he planned to run. Last September, the mayor raised more than $1 million at a Baltimore fund-raiser that was billed as a salute to his 30 years in public life, but which was viewed by contributors and organizers as a means of building a gubernatorial war chest.