The United States and the Soviet Union announced yesterday that negotiations on nuclear weapons will resume March 12 in Geneva after more than a year's suspension.

President Reagan said he will seek to reach an agreement on arms reductions during his second term but warned that the effort may take longer.

"I wouldn't try to confine it to four years, because I know how long negotiations have taken with them," Reagan said in a White House interview with radio correspondents.

The three-tier negotiations are to focus on long-range or strategic weapons, such as intercontinental ballistic missiles, bombers and submarines; medium or intermediate-range nuclear missiles in Europe; and space weapons.

Talks on both categories of missiles were suspended in 1983 after the North Atlantic Treaty Organization began deploying U.S.-built Pershing II and cruise missiles in Western Europe.

The space weapons talks are a new category. The Soviets have vowed to block Reagan's "Star Wars" missile defense system, now in the research stage. Reagan has said the non-nuclear missile defense, known as the "Strategic Defense Initiative," eventually could make nuclear missiles "impotent and obsolete."

Yesterday's announcement was made simultaneously by the White House and the Kremlin. The U.S. delegation, announced Jan. 18, will he headed by Washington attorney Max M. Kampelman, who also will represent the United States at the space arms talks.

The other negotiators will be former senator John G. Tower (R-Tex.) on long-range missiles and career diplomat Maynard W. Glitman on medium-range missiles. Paul H. Nitze and retired general Edward L. Rowny, the former long-range missile negotiator, will be advisers to Secretary of State George P. Shultz.

Officials also said yesterday that Kampelman's deputy in the space weapons talks will be Henry F. Cooper, currently assistant director of the Arms Control and Disarmament Agency for strategic programs.

The Soviet negotiating team will be headed by Viktor Karpov, who previously headed the Soviet delegation to talks on curbing long-range missiles. It also will include Yuli Kvitsinsky, who, as chief Soviet negotiator for medium-range missiles, worked on the "walk in the woods" formula with negotiator Nitze that later was rejected by both governments.

Kvitsinsky was absent from the Jan. 7-8 Geneva meeting between Shultz and Gromyko that led to yesterday's announcement.

The third Soviet negotiator will be Alexei Obukhov, deputy chief of the U.S. desk at the Soviet Foreign Ministry, who took part in previous talks on long-range missiles.

After the announcement that negotiations will resume, Reagan was asked in the interview with seven radio correspondents whether he agrees with Nitze's assessment that prospects for an agreement are better than in the past but not "very good."

"I can understand that," Reagan said, because Nitze is a veteran of past negotiations in which the United States has "gone to the table and come away without anything that was of really any great importance."

"I, on the other hand, tend to be a little more optimistic, not euphoric," he added. "I, too, know how tough this is going to be. But at least it is the first time that I can recall the Soviet Union openly themselves saying that they wanted to see the number of weapons reduced and have even gone so far to say what we have said, that they would like to see the elimination of nuclear weapons entirely."

Asked about the health of Soviet leader Konstantin U. Chernenko, Reagan said he knew "there are voices and some from within Russia" who have said "perhaps his illness is quite serious," but "I don't know" if this would affect the talks.

A White House official who spoke on condition that he not be identified said yesterday that preparations for the two missile negotiations have been "exhaustive" and are "virtually complete," and that work on the space weapons talks should be finished by the end of February.

The U.S. position has been that the talks are "interrelated," but that agreement in one area does not necessarily have to await agreement in others. Statements by the Soviet news agency Tass have indicated that Moscow believes there will have to be agreement in several areas at once.

Kampelman, in an article published last week in the bulletin of the Anti-Defamation League of B'nai B'rith, said the Soviet Union "is a threat to our values and our security. But we share the same globe. We must learn to live together. We cannot blow the Soviet Union away without blowing ourselves away with it."

Kampelman also contributed to a symposium on the future of U.S.-Soviet relations in the recently published winter issue of the Heritage Foundation's Policy Review.

"The Soviets do not appear to be restrained by the normal rules of responsible international behavior," he wrote. "Indeed one of the basic precepts of communism is that they do not have to live up to bourgeois laws or mores that are contrary to long-range interests. We therefore must question whether the Soviets would ever join us in a common effort toward peace."