President Reagan's closest friend in Congress, Sen. Paul Laxalt (R-Nev.), and top administration economic advisers appear to be lining up in support of the reappointment of Federal Reserve Board Chairman Paul A. Volcker. But White House officials said yesterday that the decision on whether to reappoint him has not yet been made.

"Volcker seems to have a lot of support," Laxalt said. "There is concern for making a change at a critical time. Wherever you go, there seems to be a lot of support. This is a change from a few months ago, when there was lots of criticism. It appears to me, from my soundings, that Volcker has rather strong support."

Treasury Secretary Donald T. Regan, who in the past has been critical of Volcker's handling of the money supply, said yesterday, "I think . . . he is an inflation fighter, and his name is associated with that. Most people give him high marks for having worked with us to bring inflation down."

The support for Volcker came from several quarters as the White House confirmed that Reagan is nearing a decision on whether to reappoint the Federal Reserve chairman. The other leading candidate for the position is said to be economist Alan Greenspan.

Volcker met with Reagan late Monday before leaving town on a fishing trip. Details of their conversation have not been made public.

Office of Management and Budget Director David A. Stockman, who is close to Greenspan, let it be known yesterday that he, too, favors the reappointment of Volcker.

Regan, in a telephone interview from New York yesterday, said that the "financial markets seem to favor him Volcker and want him by an overwhelming majority." He referred to a poll of 702 U.S. investment decision-makers conducted by the securities firm of A. G. Becker Paribas Inc. The poll found that 76.9 percent of those questioned named Volcker as the person in whom they have "most confidence" to do a good job as Federal Reserve chairman.

White House spokesman Larry Speakes said yesterday that the president has not made a decision on Volcker, but he added that it may come shortly.

Volcker, who was appointed in 1979 by President Carter, has said in recent weeks that he would like more time--a year or 18 months--to deal with the troublesome international debt situation, according to a source close to Volcker.

Under one scenario, Reagan would reappoint Volcker with the understanding that he would not serve the entire four-year term that will begin in August. That would give Reagan a chance to appoint someone of his choosing if he is reelected to a second term next year. It is not known whether the president would be amenable to such an arrangement. But administration officials are clearly not expecting Volcker to walk away from the job. They said that he did not offer to resign during his private meeting with the president Monday in the residential quarters of the White House.

One White House official said yesterday that a list of five candidates for the Federal Reserve post had been drawn up at the staff level. But other sources said that the only candidates now under serious consideration are Volcker and Greenspan.

On a policy level, the expectation among top White House officials is that little difference exists between Greenspan and Volcker. Thus, the arguments for making a change have centered on political and personality differences.

Volcker has not been personally close to the president. And Greenspan's performance in working with the administration on the Social Security Commission is one argument made on his behalf. But one informed source said yesterday that those factors may not be enough to convince Reagan to dump Volcker. That source said Volcker's reappointment would be particuarly valuable in light of the international debt crisis.

Some administration officials say they believe Reagan should appoint his own man to run the nation's central bank, which controls the money supply and influences interest rates. A congressional conservative noted, however, that Volcker has picked up support from some who earlier were critical of his performance.

Among others, Senate Majority Leader Howard H. Baker Jr. (R-Tenn.) has urged Reagan to reappoint Volcker. There has also been heavy pressure from the financial community because Volcker is seen as a symbol of resolve in the battle against inflation.