White House communications director Patrick J. Buchanan finds the differences between working for President Richard M. Nixon and President Reagan as pronounced as night and day.

Buchanan, who served as a special assistant and speechwriter to Nixon, said that oral communication is valued in the Reagan White House, while Nixon "dealt on paper a lot."

"In the Nixon administration we dealt by memoranda, I mean very candid memoranda," Buchanan said in an interview. "You put all your thoughts and arguments down . . . . This administration deals by meetings and verbal communication, even to the point of the briefing of the president.

"I used to brief Richard Nixon for news conferences and other public appearances . . . . I would send all the questions out that I had devised by reading three weeks of newspapers, news summaries and the rest of it, I'd ask the agencies and the various shops, they'd get me the material and I rewrote everything. I'd get it to Nixon. He would go into his study for eight hours and study . . . .

"With this president, you go over to the theater and maybe 10 of us are sitting there, and he's answering questions thrown up to him. It's totally different."

Buchanan, a former conservative columnist, came to the Reagan administration advocating a more confrontational approach toward Congress, the news media and various adversaries of the administration. In an interview Thursday, he did not disavow this approach but observed that the political climate is vastly different today.

"There's a sea change in terms of the mood and atmosphere of the times," Buchanan said. "That was a very tough time. Very divisive. Vietnam was on. Watergate was on. People were getting killed . . . . The relationship with the city was far more hostile than it is under Reagan. This is an era of good feeling, relatively speaking."

Since he joined the White House staff, Buchanan has been involved in every policy controversy and says he has received both blame and credit he does not deserve.

Buchanan was a leader in the successful effort to remove provisions from the tax-overhaul bill that would have taxed insurance benefits of the Knights of Columbus and other fraternal organizations. He was on the losing side in arguing for a top income tax rate of 30 percent. He also lost a battle with national security affairs adviser Robert C. McFarlane, who insisted on toning down one of Reagan's major European speeches.

Buchanan remains one of the most forceful advocates of a tough line against the leftist government of Nicaragua -- a view close to the president's. He says Sandinista actions ultimately will persaude Congress to provide aid to the rebels.

"The Sandinistas aren't going to be content to sit down there and work on their gross national product," Buchanan said. "The president's going to be proven right. We're going to win the issue, but the question is whether we're going to win it before Central America is lost."