More than 20,000 career government executives, members of Congress, judges and political appointees will get a big pay raise Sunday unless a small band of House of diehards can block the increases in a last-minute parliamentary maneuver today.

Under the law, the pay increases that former President Ford proposed in his final budget go into effect Feb. 20 unless vetoed by either the Senate or the House. The Senate is in recess and the House plans to adjourn today unless antipay raise forces can block the adjournment and/or force a record vote on the pay increase. The stategy is that many House members who favor the raises would be compelled to vote against it if they have to go on the record.

The pay increases, which President Carter has endorsed, would raise congressional salaries $12,900 a year, to $57,500. Senior employees in Grade 15 would also get increases, and all workers in GS-16, -17 and -18 would benefit.

Political appointees would get substantial increases that would raise the ceiling on the amount career government workers can get. The maximum now is $39,600, and it would go to $47,500 with the first pay period on or after Feb. 20. Most of the "supergrade" employees and political executives who would benefit from the raise live and work in the Washington area.

There is a chance - a very slim one - that the raises may be blocked today in the House. Antipayraise forces, led by Reps. Larry Pressler (R-S.D.), Robert Bauman (R-Md.) and Charles Grassley (R-lowa) will try to force a vote on the pay issue. The idea is to embarrass enough House members into voting against the raise, even though most of them probably want it.

The strategy of the antipay-raise people will be to demand a vote on a resolution killing the raises and when, as expected, that vote fails or is blocked, then to threaten to keep the House in town over the four-day Washington's birthday weekend. House leaders want to adjourn early today, but the payraise opponents will demand that it stay in session until members vote yes or no on their salaries.

If the pay raise isn't blocked today in the House, it will go into effect automatically on Feb. 20.

Democratic leaders in the Senate and House (although many Democrats oppose the raises) have done their best to keep the pay issue from coming up for a record vote. So far they have succeeded in the House, and the antipay vote in the Senate failed. With the Senate out of the picture, it will be up to the House to take action today to block its own pay raises or let them go into law automatically.