AFL-CIO President Lane Kirkland contended today that the federation's plan to to endorse a Democratic presidential candidate before the 1984 primaries is gaining union support, even though activists at the AFL-CIO regional conference here expressed some reservations.

"There is strong support that we ought to enter the primaries in a unified way," Kirkland said at a news conference. "The delegates I have spoken to have expressed . . . a strong concurrence in the desirability that we should play an effective role in the primary campaign."

The first of seven such regional conferences to be held across the country in coming months, the meeting here drew about 300 union activists from seven southeastern states for a sort of rap session unknown in the federation before Kirkland introduced it two years ago.

For school teachers, rubber workers, telephone operators and other working folks assembled here, both black and white and of all ages, it was a rare chance to ask questions and generally vent their spleen to the union brass.

The benefits to the leaders, in turn, were apparent in the phrase "I said to Lane . . . . " that was heard in the hotel hallways.

"Lane Kirkland is a common working man, not some great image out there," said Greg Stewart, a burly, bearded telephone equipment inspector from Winston-Salem and a top local union official.

Kirkland got the idea for these regional exchanges from the 1980 election, when he reportedly was stunned by Republican charges that labor leaders were out of touch with the rank and file, and by his backing a losing candidate who, it turned out, was anathema to many union voters.

The major topic was Kirkland's controversial plan for an early endorsement of a presidential candidate. Under it, the AFL-CIO General Board, made up of representatives of the affiliated unions and trade and industrial departments, is scheduled to vote on endorsement on Dec. 14 in Washington.

It requires approval of unions representing two-thirds of the AFL-CIO's 14 million members. Early surveys indicate that former vice president Walter F. Mondale would get the endorsement if the vote were held now.

Labor leaders hope that about 40 percent of the delegates to the 1984 Democratic convention will be union members, which is about the proportion of the Democratic vote of union households, according to exit polls in recent elections.

An early test of union political solidarity will come next weekend at the Massachusetts state Democratic convention's "cattle show" and preferential straw poll on presidential candidates.

The state AFL-CIO has instructed its nearly 700 delegates (about 20 percent of those voting) to show their unity by writing in "Moe Jobs" as their choice rather than any of the six active Democratic presidential candidates. They plan to do so despite a ruling by the state chairman that he will not count any of the votes for "Jobs," officials said.

Like many of the delegates here, telephone inspector Stewart's support for the endorsement stategy was qualified.

"It's a great idea, but it's so hard to get all these people to agree on anything," he said. "But unless they come up with somebody off the wall, I think we will be unified. We will get Ronald Reagan if it's humanly possible."

Some favor their home-states candidates. Karen Gabe, a high school political science teacher from Charleston and president of the Federation of Teachers local, favors her home state's Sen. Ernest F. Hollings (D-S.C.) as a candidate despite his stand against labor law reform.

"I don't support a candidate just because the national AFL-CIO does," she said. "I don't think the rank and file does."

There were indications, however, that at least some delegates felt peer pressure not to express their true feelings here.

A young Rubber Workers' union local official from Huntsville, Ala., who works at the British-owned Dunlop Tire plant, said he has worked steadily throughout the recession.

"My parents are Republican," he said. "I voted for Reagan last time and I suppose I would again."

"But," he added, "I have to say I'm a Democrat because of my union office. I'd get killed in that meeting if I said otherwise."

However, Barney Weeks, head of the Alabama Labor Council, said this was not typical of union members in the state, where unemployment has hovered near the highest in the nation.