Labor's political unity will be seriously tested in late 1983 when the AFL-CIO plans to enter national politics more vigorously than ever with a possible endorsement of a presidential candidate before the first state primary.
The federation is still smarting from poor political performances in recent presidential elections. It hopes to unify labor support behind a single candidate in an effort to influence the choice of a nominee in early 1984 at the Democratic, and possibly the Republican, convention.
An early endorsement ''is the only way we can participate effectively in the primary process,'' the AFL-CIO's president, Lane Kirkland, said during the federation's summer Executive Council meetings in New York last week.
Mr. Kirkland has asked the AFL-CIO's 99 affiliates to hold off from ''premature endorsements'' and give a mini-convention of union presidents and other leaders an opportunity to consider leading Democratic candidates and perhaps choose one for labor support in primaries and at the party convention. An endorsement by a two-thirds vote would be ''in the best interest of working people to avert political splits,'' Kirkland said.
The AFL-CIO's president said his federation might also endorse a Republican candidate ''if there is more than one in 1984.'' But he said that it is concentrating its planning now on the Democratic presidential nominee.
The plan for a possible endorsement before the primaries is a sharp break from the past. The AFL-CIO has never tried before to mobilize solid backing for a single favorite candidate before state primaries.
In breaking with the policies of his predecessor and mentor, the late George Meany, Kirkland said that past policies need to be changed because the lack of labor solidarity in the recent past was an important factor in political setbacks. In 1980, he said, ''We lost. We lost badly because we were split.''
The AFL-CIO was unhappy with the last two Democratic nominees, George McGovern and Jimmy Carter, and with the way ''liberalized'' Democratic conventions were structured. Regular party politicians and their labor allies were largely ignored in decisionmaking. As a result of its unhappiness, the AFL-CIO gave no endorsement and, Kirkland said, its affiliates ''went their varying ways.''
The AFL-CIO has worked within the party to modify convention delegate reforms. It now would like to present in 1984 a strong ''labor'' candidate for the Democratic nomination in state primaries and then at the party convention.
Plans call for a mini-convention of the AFL-CIO's general board of presidents of all federation affiliates to be held just before the first 18 state primaries. This group will not necessarily endorse a candidate. It will have the flexibility to consider first whether an endorsement would be ''desirable, feasible, and prudent,'' and then whether any candidate seeking labor support would be a strong potential nominee.
Some within labor question whether an AFL-CIO endorsement might handicap a candidate more than it would help him with the nonlabor public.