The giant AFL-CIO today is expected to give its affiliates orders to drop everything else and work on a "yes" vote in the Senate and House on legislation to give 2.6 million federal and postal workers the right to get into partisan politics.

Insiders say the monthly meeting of the AFL-CIO executive council will concentrate on drafting a strong policy statement, and strategy, to win liberalization of the Hatch Act. For the past 38 years, that law has served as an umbrella protecting government workers from arm-twisting by politicians, and it has kept civil servants from running as candidates, managing campaigns or raising funds for partisan battles.

The strong statement from the AFL-CIO will be aimed not only at Congress, which must approve the proposed changes, but at President Carter whose version of Hatch Act changes is different from the measure approved last week by a House committee.

"This is going to be more than a press release saying we want Hatch Act changes," a union official said yesterday. In effect it will be a directive to the multimillion member organization - ranging from the giant Carpenters and Electricians union to the International Association of Dolls, Toys, Playthings, Novelties and Allied Products union.

It will commit the full resources of the AFL-CIO to call in their political IOUs to get enough votes to win the liberalization of Hatch.

The big push for changes is in the main indicative of big labor's commitment to secure full political rights for the largest single group of workers in the nation - federal employees. It also is a critical test of strength for big labor, which was burned badly last month when it lost the key House vote on common-site picketing which the Senate and House cleared easily last year.

In the strange ways of politics labor leaders now worry that with a Democrat in the White House, their big 1976 vote margins might erode, even though there are more Democrats in Congress this year than last.

The thinking goes that many Democrats went along with the common-site picketing bill, and Hatch Act reform because they knew (correctly) that former President Ford would veto the measures. The idea was that they could say they voted right (with labor) but with assurance in their minds that the changes would not become law.

This year, however, President Carter said he would sign both the common-site picketing bill and Hatch Act reform when they got to him. The common-site bill lost, stunning labor, and now many leaders are afraid that congressional Democrats will defect because they know the President will sign whatever they approve.

"We are aware of the congressional waffling on the Hatch Act this time," a postal union leader said, "and we've been pushing the council for a flatout, no-quarter statement putting members of Congress on notice that we will be watching them closely on this one. We don't want anybody out of the room when this vote comes up."