The Labor Department's 15,200 enployees - including 6,400 who work in the Washington area - were warned yesterday that their next pay checks probably will be cut in half because of a congressional battle over a bill that would pay their salaries.

About 132,500 employees of the Department of Health, Education and Welfare - among them 34,000 in the Washington area - may also face similar pay reductions, government officials said yesterday, unless a congressional breakthrough occurs within a few days.

The grim and highly unusual prospect of reduced mid-October paychecks - which has stirred an outPouring of worries and complaints among Labor and HEW employees - stems from a continuing clash between House and Senate members over federal financing for abortions. The abortion controversy has blocked congressional action on this year's $60.1 billion Labor-HEW appropriations bill.

In a memo circulated yesterday, the Labor Department warned its employees that their Oct. 17 pay checks will be reduced unless President Carter signs an appropriations bill by next Tuesday. Labor's announcement, however, followed a House subcommittee decision to postpone further voting on the disputed measure until next Wednesday or later, apparently missing Labor's salary deadline.

Even if the House votes next Wednesday on an abortion provision, prospects for enactment of a Labor-HEW money bill remain uncertain. The Senate repeatedly has balked at House attempts to set stringent restrictions on federally financed abortions.

An HEW spokesman said that HEW's next salary deadline is Wednesday. Unless Congress approves an appropriations bill by then, the spokesman said. HEW employees may receive only half their pay on their Oct. 18 pay checks.

The two departments' authorization to spend money expired Sept. 30, the end of the last fiscal year. Because of Congress' failure to appropriate new funds for the current fiscal year, Labor and HEW already have ended all hiring and overtime pay and eliminated most out-of-town travel.

Mid-October pay checks for Labor and HEW employees normally would include their salaries for the last week of September and the first week of October. Because Congress' failure to appropriate money for the fiscal year that began this month, department spokesmen said, employees may only be paid for the last week of September.

The Treasury Department which sends out government pay checks, added one brighter note to yesterday's increasing gloom over Labor and HEW salaries. A Treasury official, who asked not to be identified, said that attempts would be made to avoid trims in pay checks even if Congress fails to meet the normal salary deadlines for Labor and HEW.

"In a situation like this, we would work overtime," the Treasury official said. "We would work weekends and things like this."

As government officials continued to meet yesterday amid deepening concern over the pay check outlook, it remained uncertain how much delay the congressional logjam would cause in the issuance of Labor and HEW pay checks. When Congress eventually approves a Labor-HEW appropriations bill, officials say, retroactive pay checks will be sent out, if necessary.

The House had been expected to vote this week on a proposed abortion amendment to the Labor-HEW appropriations measure. The amendment, drawn up after the House rejected a Senate-proposed compromise, would permit federal payments either for abortions intended to save a woman's life or for what was termed "prompt treatment" - rather than abortions - after a rape or incest occurs.

The expected House vote was postponed until next week, according to conference committee sources, because the House amendment's proponents feared it would be defeated, partly because of opposition by antiabortion groups. The delay apparently will allow time to seek additional support.

While Labor and HEW financing could also be extended if Congress passed what is known as a continuing resolution. House Appropriations Committee Chairman George H. Mahon (D-Tex.) has opposed such a resolution, saying it would fail to settle the abortion dispute and might stir a controversy of its own.