President Reagan returned from his California vacation last night, facing a decision on his embattled national security adviser, Richard V. Allen, and a meeting with West German Chancellor Helmut Schmidt.

White House deputy press secretary Larry Speakes told reporters on Air Force One that Reagan will not meet with Allen today, as had been expected, but will see him later in the week.

He said presidential counselor Edwin Meese III talked to Allen on the telephone yesterday "in general terms about a determination" of the Allen matter.

Allen has been on administrative leave with pay pending a White House review of his conduct in accepting a $1,000 honorarium from a Japanese magazine and three gift watches from Japanese friends.

Speakes said he could not predict whether the internal review would be completed by the time Allen meets the president, although he said it is quite possible it will be.

Reagan is expected to put Deputy Secretary of State William P. Clark in Allen's job, and to try to bring some order to his White House foreign policy-making apparatus by giving Clark expanded powers, including direct access to the president.

When asked yesterday who would replace Clark at the State Department, Speakes said: "I haven't even heard any good rumors."

Reagan refused to comment on the Allen matter as he was boarding Air Force One in California yesterday for the return trip. Allen could not be reached for comment, but he said Friday that he had not been informed of any plans to replace him.

The president also will try to deal this week with another foreign policy headache--the matter of winning support from its allies for U.S. sanctions on the Soviet and Polish governments in response to a crackdown on the Solidarity movement in Poland. Reagan's meeting with Schmidt Tuesday is expected to focus on the issue.

Like other European allies, Schmidt has described the crisis as an internal Polish dispute and has suggested that U.S.-imposed economic sanctions may be counterproductive. The chancellor, who is vacationing in Florida before his meeting with Reagan, said last week that West Germany would "find it very difficult" to impose sanctions.

A similar viewpoint regarding sanctions was offered yesterday by George F. Kennan, former U.S. ambassador to the Soviet Union.

"It's very difficult for me to see that any positive results could be obtained from the sanctions imposed on the Soviet Union," Kennan said on "Meet the Press" (NBC, WRC). He said the U.S. sanctions "are mere pinpricks" to the Soviets that "have heightened the tensions and the ill feeling between the two governments."

Kennan, an authority on American relations with the Soviet Union, said, "there are limits to what we can do about the Polish situation."

"I am persuaded that if these reform movements continue to proceed gradually, without raising abrupt challenges to Soviet prestige . . . they can continue to make good progress--as indeed they have done to date," he said.

But former national security adviser Zbigniew Brzezinski, interviewed yesterday on "Face the Nation" (CBS, WDVM), said the United States should increase economic sanctions against the Soviet Union "if the suppression of Solidarity and Polish society continues." For example, cutting of phosphate deliveries to the Soviets "would be a signal that we might be moving further in the future if the Soviets were to become actively involved" in Poland, he said.

Brzezinski said the Schmidt meeting is important because it will give Reagan a chance to argue that German hopes for reunification, as well as the future of East-West relations, are at stake in the Polish crisis.

"If the situation in Poland degenerates into massive suppression, perhaps even Soviet intervention, then that will be the last nail in the coffin of German hopes for reunification. The Germans should have no illusions that what is happening in Poland somehow leaves the fate of Germany, particularly East Germany, unaffected," Brzezinski said.