An annual convention of Maryland labor leaders opened here today amid sharp divisions over whether to proceed with a planned endorsement of Attorney General Stephen Sachs' gubernatorial candidacy.

The endorsement would bring Sachs the support of the 425,000-member Maryland State and District of Columbia AFL-CIO and would be an early boost for him.

Sachs, according to preliminary polls, distantly trails Baltimore Mayor William Donald Schaefer, who has not formally announced his candidacy for the 1986 race.

State labor officials have suggested for several weeks that they would hand the endorsement to Sachs this week; but on Friday several prominent Baltimore labor unions, some of whom are on the verge of beginning contract negotiations with Schaefer, said they would try to forestall the move.

They argued they have not polled their members and noted that some potential candidates have yet to declare. The dispute remains to be worked out during a general session Tuesday.

"We haven't made up our minds about what we're going to do," said Irene Dandridge, president of the 6,500-member Baltimore Teachers Union, and part of a group trying to forestall the endorsement. "Right now our concern is we don't want an endorsement this early."

Said Alan Knott, a leader of the Ironworkers Local 16, "We are going ahead with it an endorsement , at least the ironworkers are. He Sachs is aware of the needs of the working-class people . . . ."

Schaefer has a history of chilly relations with leaders of organized labor, most recently teachers and the building-trades unions, most of whom bypassed a million-dollar fund-raiser for him last month.

Maryland AFL-CIO President Edward R. Lamon said Schaefer's attitude toward labor was illustrated by his refusal Sunday to be interviewed for the endorsement, as did Sachs and Maryland House Speaker Benjamin L. Cardin, the third candidate in the Democratic race.

Lamon said he considered an endorsement likely because "a lot of people are leaning that way." Privately, another executive board member said, "the votes are there" for Sachs.

To receive the endorsement, a candidate must receive the recommendation of the executive council, and then at least two-thirds of the votes of the expected 300 delegates, who represent union locals from throughout the state and the District.

Candidates, particularly those seeking state and federal offices, place great value on labor's support, and the union has a good record of choosing winning candidates in the Democratic primary.

Mindful of that, nearly every member of the state's congressional delegation and many candidates addressed the convention today or are scheduled to speak later, including U.S. Democratic Reps. Michael Barnes and Barbara Mikulski, both of whom will be running for the Senate next year.

Schaefer also addressed the group. He stressed what he said was a record of positive labor relations, saying, "We've done more for city workers than any other previous administration."