Triggered by a dramatic vote shift in the House. Congress broke a five-month deadlock yesterday and adopted liberalized rules for federally financed abortions.

The congressional action remove a threat of short pre-Christmas pay-checks for thousands of employees of the U.S. departments of Labor and Health, Education and Welfare, whose budgets were stalled by the abortion issue. The action also renewed the lapsed spending authority of the District of Columbia.

In the last full year before federal Medicare funding was cut off, about 300,000 women underwent abortions under the program. Sen. Edward W. Brooke (R-Mass.), a leading advocate of liberalized policy, voiced a guess yesterday that about 100,000 women a year may get abortions under the new procedures.

Despite the softening of the House's hard-line position, proabortion groups remained dissatisfied. The 20,000-member National Abortion Rights Action League called the action "inhumane . . . restrictive . . . quite possibly unconstitutional . . . costly."

The final break in the emotional, politically volatile issue of Medicaid abortions - chiefly for poor women - came in the second of two roll-call votes taken within four hours yesterday in a House whose memebers were obviously growing weary of the issue.

The first time, House memebers voted 178 to 171 to stand by their strict position against all federally funded abortions, except those needed to save a mother's life.

Appropriations Committee Chairman George H. Mahon (D-Tex.), who had described himself as "depressed" and "glum" over the issue, huddled with colleagues, drafted new language, won a speedy approval for it from the Rules Committee and marched back onto the House floor.

There, after brief debate - and with restless members calling, "Vote! Vote! Vote!" - the House reversed direction and adopted the new and looser rules, 181 to 167.

Within two hours, with only six of its members on the floor, the Senate agreed to the House action and sent the measure to President Carter for his signature.

Technically, the measure is a "continuing resolution," which provides operating funds for the departments of Labor and HEW and for the D.C. government until Sept. 30, 1978, the end of the current fiscal year.

The legislative path that led to the adoption of the resolution, an unusual procedure, began when the House voted to attach the so-called Hyde Amendment to the Labor-HEW budget bill last June.

The measure, named for Rep. Henry J. Hyde (R-III.), barred all Medicaid abortions except those needed to save a mother's life. The Senate refused to accept it. A House-Senate conference committee could not agree on suitable language before the start of the new fiscal year Oct. 1.

When the need arose for a stopgap resolution to continue funding for Labor and HEW into the new fiscal year debate again centered on the Hyde Amendment. So the interim measure finally evolved into the final $60.2 billion budget for the two agencies that was enacted yesterday.

As finally approved, the legislation permits Medicaid abortions in three situations:

Where the mother's life would be endangered if the fetus were carried to term.

Where there has been raped or incest, reported promptly to a law enforcement or public health agency.

Where severe and long-lasting physical health damage would result in the mother if the prgnancy were carried to term, when such circumstances are determined by two physicians.

The language requiring the health determination by two physicians was added by Mahon and his colleagues between the two House votes and was credicted by him with bringing the switch in votes. Mahon said it would reduce Medicaid fraud.

Rep. Tim Lee Carter (R-Ky.), a physician who said he opposes aboriton in his won practice, said he was persuaded by that language. Rep. Carter was the last to speak before the final House vote.

The stage was set for yesterday's actions by votes Tuesday in the House and Senate. Although contradictory in content, the nature and outcome of the votes suggested that a compromise might at hand.

Yesterday, it was the House's turn to consider the Senate's most recent proposal, to required prompt reporting of rape or incest as a condition for getting an abortion under Medicaid.

Hyde, author of the amendment bearing his name, enchoed the stand of right-to-life groups by contending the measure "provides for the extermination of thousands of unborn lives."

But, Hyde added, "I don't like to be the consummate Christmas Scrooge, standing between thousands of (federal) employees and their Christmas paychecks."

The first roll call, taken by an electronic device and lasting 15 minutes, was agonizingly close until the final minute, when the tally stood 164 to 164. As time ran out, the opponents pulled ahead, 176 to 172. With a few vote switches, the final tally was 178 to 171 against the Senate proposal.

House Speaker Thomas P. O'Neill (D-Mass.) looked on , not voting and taking no open role.

The debate before the second vote was deculetory, Rep. Robert E. Bauman (R-Md.), a leading supporter of the Hyde Amendment, accused mahon of engineering a "complete betrayal." Once the second roll call began, is outcome was never in doubt.

The Senate, which had recessed from hour to hour all day, awaiting the House action, quickly convened and concurred. Sen. Warren G. Magnuson (D-Wash.), acting chairman of the Appropriations Committee, offered the motion, and Brooke described the outcome as "not really acceptable to either side, but it maks some progress."

Sen. Jacob K. Javits (R-N.Y.) said the congressional action was "a victory for humanity and enlightment . . . a major victory for women's rights."

Arych Neier, executive director of the American Civil Liberties Union, in a statement issued later, said the congressional action was no compromise. "It is a brutal treatment of women with medical needs for abortions . . . This law denies women the right to control their destiny."

For 17,000 employees of the Labor Department yesterday's action came too late to assure full paychecks this week.A spokesman said the missing 20 per cent of each employee's salary will be paid in a supplementary chec to be mailed this weekened. Howere, HEW employees were assured full pay checks by the congressional action.

The measure provides financing for the D.C. government at last year's level until next Sept. 30, but does not restrict the right of a House-Senate conference committee to enact a regular budget in the meantime.

Following are the the votes of Maryland and Virginia House members on yesterday's second roll call: