The AFL-CIO adroitly passed a key credibility test at the state Democratic convention here Saturday, keeping its troops locked in a political chastity belt against the ardent advances of presidential candidates and their various allies.

The spectacle also provided an early sampling of tensions and conflicts that the blossoming liaison between the labor federation and the Democratic Party may hold.

Labor leaders considered a strong showing here essential to persuade a skeptical political establishment that, after years of fragmentation and drift, "labor can deliver." Among other things, their well-orchestrated performance is likely to enhance substantially the value of the AFL-CIO's planned endorsement of a presidential candidate by the end of this year.

"We need to show the political managers and campaign staff of various candidates that labor can act united and that there is discipline," said John Perkins, director of the AFL-CIO's political arm, the Committee on Political Education, who observed the proceedings from the convention floor.

"Some candidates may be discouraged by what they see us doing here today. But down the road, I think they'll find it will be beneficial."

The labor "candidate" here was an issue entitled "Jobs," which with 25.6 percent of the vote finished a healthy second to former vice president Walter F. Mondale's 29.3 percent in the non-binding poll. Sen. Alan Cranston (Calif.) was third.

Mondale is considered most likely to win labor's endorsement and, to make the point that he would have gotten most of the "Jobs" votes, his supporters distributed buttons claiming "Jobs Equal Mondale." Supporters of Cranston, a strong labor ally, argued that at least some of those votes would have been his.

Although the exact breakdown was not immediately known, the 884 votes for "Jobs" apparently comprised not only virtually all of labor's nearly 700 delegate votes but others from non-union delegates who, for various reasons, found "Jobs" an appealing haven for now. A total of 3,830 delegates voted.

Among those who had indicated that they might join labor and vote for "Jobs" were nuclear-freeze delegates, who wore "Jobs and Peace" buttons, and state representatives of the National Education Association. NEA, like the AFL-CIO, is trying to stay neutral until making an official national endorsement.

Besides maintaining labor's position of official neutrality in the presidential sweepstakes, the strategy also made jobs and unemployment the dominant topic at the convention in a state where the unemployment rate is a relatively low 7.8 percent.

State Democratic Party chairman Chester G. Atkins said that a strong vote for "Jobs" indicated that none of the candidates had electrified the crowd and that delegates were concerned more about economic renewal than about personalities.

On the way to its "Jobs" vote, labor and the Democrats ran a gantlet of pressures of the kind that may intensify as the campaign season heats up.

In the weeks before Saturday's vote, Mondale supporters, including some unionists, looked for ways to head off the labor scheme, since their candidate could be expected to lose the largest share of votes to it. The strategy was awkward.

"You don't want to collide with people legitimately going about their institution-building and clout-building," Mondale operative Paul Tully told The Boston Globe. But, he added, "This operation scares me to death because I'm losing a big chunk of votes here."

A Globe columnist, among others, took labor officials to task for putting their presumed candidate in such a position.

Earlier this month, party chairman Atkins stood against the labor strategy by ruling that votes for "Jobs" would not be counted. At the last minute, party officials backed off and worked out a rules change.

Gov. Michael S. Dukakis (D), who had numerous supporters among the delegates, was credited with triggering the turnaround by sending his new secretary of labor, Paul Eustace, to accompany state labor council head Arthur Osborn to a meeting with Atkins to discuss the issue.

Some campaign operatives and party officials said the reversal came partly because they were convinced that labor was serious and would go ahead with its plan no matter what. But labor received help from other Democrats upset that what was supposed to be an issues convention was turning into a so-called "cattle show," by some accounts.

In any case, Mondale operatives said they continued to work on delegates, gingerly, until the moment of the vote. The pressure was evident even during the voting, a roll call voice vote by state Senate districts.

The state organization had started early and worked hard to "get lean and mean," labor officials said, tripling union delegate strength compared with two years ago. As early as January, leaders had summoned the union legions through blizzards to frequent meetings and worked to improve communications and "outreach" to their members, according to unionists at various levels.

The notion of voting for "Jobs" was dreamed up by state AFL-CIO leaders and not, as some assume, imposed by AFL-CIO President Lane Kirkland, according to Osborn. "We had the idea, after listening to the goals of our national leaders," he said. "It was something we could give them as a model."