President Reagan, trying to dampen expectations of a quick arms-control deal with the Soviet Union, warned today that any agreement will involve "hard bargaining" over a long period of time.

Reagan's cautious appraisal of the likely results of the Jan. 7-8 meeting in Geneva between Secretary of State George P. Shultz and Soviet Foreign Minister Andrei A. Gromyko was contained in written responses to Japanese reporters who interviewed him in the Oval Office last week.

Administration officials said the text of the interview with the newspaper Yomiuri Shimbun was released today while the president is vacationing in California in an effort to lower expectations about the talks.

The Soviets have done "a skillful job of trying to regain the propaganda offensive" on arms control, said one official, who referred to the positive reception given Soviet Politburo member Mikhail Gorbachev on his recent visit to Western European capitals.

In the interview, Reagan said he was "encouraged" by the Soviet agreement to resume a dialogue on arms control.

"But we must temper our expectations with realism," he added. "A two-day meeting cannot solve the complicated issues before us. We hope it will be a constructive beginning for further, detailed negotiations. But it isn't an easy job. Only time will tell how rapidly the process moves, or in what specific framework."

A similar note of caution was sounded by White House spokesman Larry Speakes today. In his only briefing of the week, Speakes read a statement saying that the administration could not predict the outcome of the talks.

"We go into the meeting with high hopes but no pre-conceived expectations," he said. "We've recognized that there's hard bargaining which lies ahead. We cannot solve the complex issues entirely in a two-day meeting, but we can make a start."

Speakes said Reagan will receive recommendations over the weekend concerning the U.S. position at Geneva; the recommendations were prepared by Shultz, national security affairs adviser Robert C. McFarlane and others.

The spokesman said the president may also meet in California this weekend with Shultz, McFarlane and Secretary of Defense Caspar W. Weinberger.

Reagan and several Cabinet secretaries, including Shultz and Weinberger, are to attend an annual New Year's Eve party at the home of publisher Walter Annenberg.

The U.S. official who spoke of the Soviet "propaganda offensive" expressed the view that the Soviets seemed more interested in trying to create fears about the president's Strategic Defense Initiative, a research program often referred to as "Star Wars" that is aimed at intercepting incoming missiles in space.

Speakes, picking up the language of a reporter's question, said the president is "not going to change his position on "Star Wars,"" a point made last weekend by Weinberger and McFarlane in television interviews.

But Reagan did not mention the research program in his interview with the Japanese newspaper, and officials said the U.S. focus at Geneva would be on the necessity of limiting offensive nuclear weapons.

Reagan did discuss an issue of importance to the Japanese in the talks on intermediate-range nuclear weapons. The Soviets walked out of those talks a year ago to protest the deployment of Pershing II and cruise missiles in Western Europe.

During those talks, the Japanese wanted assurances, which they received from Reagan, that no agreement would be reached that allows the Soviets to transfer their missiles from Europe to Asia, where they could be aimed at Japan and other Asian nations.

Reagan said in the interview that the Chinese "are very positive about our forthcoming arms talks with the Soviets" but "don't want the Soviets to redeploy their missiles from west to east. We agree."