President Reagan has contended that the current economic recession "might not have happened" if Congress had been willing to allow his large tax cut package to begin retroactively from last Jan. 1, as he originally proposed.

The president sought to direct blame for the recession that now plagues his administration upon Congress' insistence that implementation of the tax cut be delayed until Oct. 11 during an interview with Gerald E. Udwin, vice president and Washington bureau chief of Westinghouse Broadcasting Co. The interview was taped last Monday and Tuesday in the White House library for airing next Monday. A copy of the transcript was made available to reporters yesterday.

In the interview, Reagan noted that he had proposed first that the tax cut begin as of Jan. 1, and that when Congress balked, he had sought a compromise starting date of July 1. "I still believe that, had we gained one on either one of those points, January or July, that this recession might not have happened," the president said.

He also explained why he now feels it "isn't as important" to have the budget balanced by 1984 as he used to say it was when he committed his administration to that now-discarded goal. "I am still convinced that even though the deficits now loom as larger than the administration anticipated and we may go beyond 1984, that isn't as important as getting inflation further down, unemployment further down, and interest rates further down," Reagan said.

The president also talked publicly for the first time of his confrontation in the Oval Office with his two frequently feuding foreign policy advisers, saying he told Secretary of State Alexander M. Haig Jr. and national security adviser Richard V. Allen "in effect--and said more politely and more eruditely--to 'Shut up.' "

Reagan said he told Haig and Allen what he has told other Cabinet officers: "You've got to be extremely careful. And you've got to tell the people in your departments, you've got to tell them that there is no such thing as a secret, that they've got to be very careful of what they say and how they say it. And I think I let them know that I was a little impatient with what I thought was not talking with a single voice, but . . . a kind of babble . . . taking place."

Reagan still maintained that news reports of the friction that has existed since inauguration day among members of his national security high command "has been exaggerated out of all limits." He added: ". . . even in state government, while there were leaks, I never experienced the kind of gossip that then becomes taken as general news with distinguished journalists lending themselves to it."

As the president sees it, all has been tranquil on the advisory front. "There has never been any animus that I've detected," said the president. "There's never been any personal animosity between any of the people in these debates and discussions . . ."

He also said that he is not isolated in his job. "You aren't that isolated, as much as you think," the president said. "You make appearances at various kinds of gatherings and so forth. And very often, while you don't get to say hello to 2,000 people in a banquet hall, before and after you do talk to many of those people."

He also said he reads a portion of the mail that comes from the public. And he added that when he goes home to his ranch in California, it helps him keep in touch with the cross-section of American opinion. He said: ". . . suddenly you're back with the veterinarian that comes to see the horses and the fellows that deliver the feed and the fellow that works for you and your neighbors . . ."

When the interviewer suggested that Reagan's predecessor, Jimmy Carter, was probably more "open-minded" but that Reagan was "more decisive," the president said: "I have an open mind. I really do."

He went on to explain: "On the other hand, I have some firm convictions." And he cited his policies on the air traffic controllers strike and on the Soviet Union as two examples.

On the controllers strike, he said "the law is very specific. It is illegal for them to strike." And of the Soviets, he said "they are the ones who have said their goal is world communism, that they are going to impose their will on the rest of the world. And it's a little bit like that strike situation. I have to say, 'No, they're not'."

And as his predecessors, Reagan has come to feel that one of the greatest frustrations of the presidency is the bureaucrats, "far down into the permanent structure of government." He added: ". . . in government, there is a tendency on the part of some people . . . in the permanent structure, that they've been here before you got here and they'll be here after you're gone and they're not going to change the way they're doing things."