President Reagan eased one set of problems but may have exacerbated another with his announcement yesterday that he was dropping his sanctions against construction of the Soviet gas pipeline to western Europe.

The sanctions had been a political albatross for Reagan in the Midwest, where thousands of unemployed Caterpillar Tractor Co. workers in Peoria, Ill., personified the domestic costs of his hard-line approach to the Soviets.

They had also seriously complicated U.S. relations with the allies in western Europe, who want the pipeline built and NEWS ANALYSIS in any case resent U.S. interference in what they regard as their internal affairs.

Reagan helped smooth out both these problems yesterday.

His announcement may also, in the eyes of many people, help him past an awkward point in U.S. relations with the Soviet Union.

Though apparently not meant that way, it could be construed as an olive branch of sorts toward the Soviets at just the time their own leadership is changing.

Reagan himself acted to reinforce this impression yesterday.

Asked as he left the White House after his announcement what signal he intended to send the Soviets by his decision, Reagan said:

"I hope the signal will be that we are ready for a better relationship any time that they are."

And before his radio address, Reagan visited the Soviet Embassy to express condolences on the death Wednesday of Soviet leader Leonid I. Brezhnev.

During a six-minute visit, Reagan wrote in the book of condolences:

"My condolences to the family of President Brezhnev and the people of the Soviet Union. May our two peoples live in peace in the world together. Ronald Reagan."

But while some may regard it as good if Reagan is easing up a little in approaching the Soviets, others will not -- and that is the problem his announcement yesterday may exacerbate for him.

Depending on what happens next in U.S. and European trade policy toward the Soviet Union, conservatives could end up accusing Reagan of having retreated on an issue of major importance to them.

The question is whether hard-lining loyalists will decide Reagan has wavered in dealing with the Soviets and Europeans without gaining significant concessions in return.

That will depend in large part on what specific policies come out of the studies that Reagan said yesterday will now be undertaken in various areas of trade, whether he has really succeeded in raising allied consciousness on this issue or whether, now that he has dropped his sanctions, the allies will return to business as usual.

East-West trade is not the only issue on which conservatives now are fearful Reagan is straying.

They complained when he advocated a tax increase last summer and are afraid he may agree to moderate his defense buildup next year, for example.

These conservatives are important to Reagan, both symbolically and because they have always been the heart of his support.

But Reagan can also afford to offend them now and then.

Rail at him though they sometimes do, in national politics they have nowhere else to go.