A House committee yesterday reversed itself and approved an amendment to President Carter's civil service overhaul bill that would revise employes to take active roles in partisan politics.

The House Post Office and Civil Service Committee had defeated the amendment by one vote the day before. Yesterday's switch followed a series of misunderstandings and delaying tactics by members that, among other things, involved a spat between organized labor and its supporters on the committee.

The amendment was virtually the same as a controversial bill that passed the House last year with the backing of the Carter administration and organized labor but was stalled in the Senate.

The Carter administration, some members of the committee and some union representatives said they support the Hatch Act revisions but oppose, on tactical grounds, tying them into the civil service overhaul issue.

The White House issued a statement after yesterday's committee action indicating that President Carter is "disappointed" and will urge the full House to separate the two issues again when the bill reaches the floor.

The committee vote reconsidering the amendment was 13 to 10. Votes needed for passage were picked up after labor lobbyists moblilzed belatedly in support of the amendment, sources said.

Union spokesmen and their supporters said they are skeptical of the president's "sincerity" in pushing the Hatch Act revisions and talked about using the amendment as leverage to force the president to "spring loose" the revisions being held up in the Senate.

Republicans who have been supporting civil service revisions reportedly considered attempting to hold that bill hostage in the Senate to prevent the Hatch Act changes from proceeding to the House.

The amendment's sponsor, Rep. William Clay (D-Mo.), a staunch ally of labor, and others on the committee had been outraged" at reports Wednesday that union lobbyists had been telling members to vote against tying the Hatch changes to civil service revision bill.

In retaliation, Rep. Charles Wilson (D-Calif.) halted a committe markup session on the bill in mid-debate yesterday morning by invoking a House rule preventing such sessions when the full House meets.

Wilson allowed the committee to proceed only after Clay convinced him that the earlier "misunderstanding" with unions had been resolved and that they had the votes needed to win adoption of Clay's Hatch Act changes, according to a Wilson aide.

Committee Chairman Robert N. C. Nix (D-PA) switched his vote to favor the amendment yesterday; and Reps. Gladys Spellman (D-Calif.), who had not voted Wednesday, voted for the amendment yesterday. Rep. Herb Harris (D-Va.) did not vote either day on the Hatch changes.