President Reagan remains convinced that many New Deal advisers to President Franklin D. Roosevelt espoused fascism and spoke admiringly of Mussolini's Italian fascist regime.

Reagan was attacked during the 1980 campaign, principally by Sen. Edward M. Kennedy (D-Mass.), for holding the view that "fascism was really the basis for the New Deal." It is an idea Reagan first voiced in 1976 and has repeated several times, most recently in an interview with Ben Wattenberg to be broadcast on the Public Broadcasting Service Friday night.

The president says that Roosevelt was not one of those who espoused fascism, but that many New Dealers "spoke admiringly of how Mussolini had made the trains run on time."

"In other words," he continued, "they saw in what Roosevelt was doing, a planned economy. Private ownership, but government management of that ownership and that economy."

The president added that "Harold Ickes Roosevelt's secretary of the interior , in his book, said that what we were striving for was a kind of modified form of communism."

Reagan does not amplify these remarks except to say that "I don't believe that that was really in Roosevelt's mind."

His remarks to Wattenberg are not as clear as his statement at a news conference last August when he told a questioner that "anyone who wants to look at the writings of the Brain Trust of the New Deal will find that President Roosevelt's advisers admired the fascist system . . . . They thought that private ownership with government management and control a la the Italian system was the way to go, and that has been evident in all their writings."

Reagan has not cited a reference in the writings of the Brain Trust and research efforts have failed to find any. John P. Diggins, whose "Mussolini and Fascism: The View from America" is regarded as the definitive scholarly work on American views toward Mussolini, wrote: "The published writings of the Brain Trusters reveal no evidence of the influence of Italian fascism upon the New Deal."

Diggins added that such an accusation was made by both left and right during the 1930s.

In the 1930s, Reagan was a Roosevelt Democrat. When he first voted in a presidential election, he voted for FDR in 1932.

"The Roosevelt I voted for had promised to cut federal spending by 25 percent," Reagan, who worked hard this year to reduce the rate of federal spending growth, recalled.

In addition to linking the Brain Trust to fascism, Reagan reiterated another belief that many dispute during the interview with Wattenberg.

He said that recent antiwar demonstrations in Europe were Soviet-backed.

"Oh, those demonstrations. You could have used newsreels from the '60s in America. Yes. Those are all sponsored by a thing called the World Peace Council, which is bought and paid for by the Soviet Union. And my only question to those young people, and I know that many of them are very sincere, but why aren't there such demonstrations going on in the Soviet Union?"

Reagan added that there haven't been so many demonstrations since he made his proposal on Nov. 18 for limiting intermediate-range nuclear weapons in Europe.