Liberals on the House Ways and Means Committee are mounting an effort to include repeal of major foreign tax breaks for U.S. oil companies as part of the "windfall profits" tax bill the panel will take up next week.

The liberals lost an initial bid when their plan was defeated by a caucus of panel Democrats in a secret meeting on Wednesday, but spokesmen said they plan to try again when more of the committee's members can be present.

Meanwhile, panel sources said the caucus vote showed committee Democrats were more adamant than had been expected about stiffening President Carter's "windfall profits" tax proposal, and may tougthen the measure sharply.

The panel plans to begin drafting the "windfall" bill next week in hopes of bringing it to the floor by June 15. However, if the liberals' bid to include repeal of the foreign tax breaks succeeds, the measure could be delayed.

The move by the liberals has run into opposition from Rep. Al Ullman (D-Ore.), the panel's chairman. Ullman fears that loading the "windfall profits" bill with extra provisions could break its momentum and jeopardize passage.

However, the liberals contend their case was strengthened by a House floor vote during consideration of the new congressional budget resolution in mid-May in which the lawnmakers cast a protest vote to repel oil-firm tax breaks.

Although the vote did not actually alter present law any, the liberals say it amounted to a mandate from the full House. The action, which involved the foreign tax credit for oil companies was regarded as a political gesture.

Ullman has been arguing repeatedly for a prompt - and decisive - vote on a "windfall profits" tax bill alone. He even presuaded the White House to defer sending up its own companion proposals on the oil credit until the first bill is through.

It was not immediately clear from the caucus Wednesday just how far the panel's Democrats wanted to go stiffening Carter's proposal for a "windfall" tax. The president's plan is considered mild by most outside observers.

The vote against the liberals' plan Wednesday was 9 to 7. However, several key Democrats reportedly were absent from the session. Liberal leaders said yesterday they hope to round up the 13 votes needed for a majority.