President Reagan has agreed to a plan to increase the power of his national security affairs adviser and will name Deputy Secretary of State William P. Clark to replace Richard V. Allen in that post early this week, senior administration sources said last night.

The sources said Reagan tentatively made the decision after a lengthy meeting with close political advisers in Palm Springs, Calif., yesterday. However, the sources continued, the president wants to defer a formal announcement until after his return here today and further discussions with advisers, including presidential counselor Edwin Meese III, who was not present at the Palm Springs meeting.

Reagan met yesterday with Secretary of State Alexander M. Haig Jr. for 30 minutes at the estate of Walter Annenberg, where the president is a guest. They were later joined by Clark and White House deputy chief of staff Michael K. Deaver.

Barring the unexpected, the sources stressed, Clark will be named--possibly on Monday or Tuesday--to the restructured security adviser's post with powers that will put him at the top levels of the White House decision-making process.

It was reported that Allen had asked to meet with the president on Monday.

The sources said no decision has been made about Clark's replacement as principal deputy to Haig. But, they added, those under discussion as potential replacements are U.N. Ambassador Jeane J. Kirkpatrick; James L. Buckley, undersecretary of state for security affairs; and Lawrence A. Eagleburger, assistant secretary for European affairs.

The decision to replace Allen and upgrade the security adviser's job was motivated partly by the problem of Allen's recent difficulties over his receipt of a $1,000 honorarium from a Japanese magazine and partly by a consensus in the White House top echelon that the national security apparatus had not worked effectively during Reagan's first year in office.

Allen, who reported to Reagan through Meese, was far more circumscribed in his authority than previous occupants of the post.

Allen is on administrative leave and was cleared recently by the Justice Department of allegations involving his receipt of the $1,000 and of three watches, as well as questions over his financial disclosure statements. He is still awaiting a final White House review of the propriety of his conduct.

It was not immediately clear whether Allen will be offered another job in the administration if the review absolves him.

Under the new system, tentatively approved by Reagan yesterday, the sources said, the national security adviser will have direct, day-to-day operational responsibility for all matters involving foreign relations, defense and intelligence. He will meet daily with the president and will deal directly with Haig, Defense Secretary Caspar W. Weinberger and CIA Director William J. Casey.

The practical effect of this new division of responsibilities will be to put Clark on a par with the triumvirate of Meese, chief of staff James A. Baker III and deputy chief of staff Deaver, who have run the White House policy-making and daily operations.

This upgrading represents a turnabout from the administration's original desire to avoid concentrating so much authority in the national security adviser's job. Instead, Allen had been subordinated to Meese in the hopes of averting the kinds of conflicts that occurred in previous administrations between the national security adviser and Cabinet officials.

However, senior officials revealed last week that it had been decided that the national security policy-making machinery had become bogged down in confusion and lack of coordination because there was no single focal point in the White House for contact with top officials of State, the Pentagon and the CIA.

In addition, the situation had been compounded by personality conflicts between Allen and other officials, most notably Haig.

Clark, 50, is a former California Supreme Court justice and a long-time political associate of the president. He served as Reagan's first chief of staff while Reagan was governor of California in the 1960s.

Clark had no experience in foreign policy when he came to Washington and was criticized heavily for showing an embarrassing lack of expertise in international affairs during his Senate confirmation hearings last February. In the months since, however, he has carved out an important niche at the State Department through his ability to mediate between Haig and such old political associates as Meese and Deaver at the White House.