Secretary of State George P. Shultz and Soviet Foreign Minister Andrei A. Gromyko will meet in Geneva Jan. 7 and 8 to arrange an agenda for new negotiations to control nuclear arms and space weapons, the two governments announced yesterday.

Robert C. McFarlane, President Reagan's national security affairs adviser, and Vladimir Lomeiko, spokesman for the Soviet Foreign Ministry, held simultaneous news conferences in Washington and Moscow to announce that the two sides "have agreed to enter into new negotiations with the objective of reaching mutually acceptable agreements on the whole range of questions concerning nuclear and outer space arms."

McFarlane told a Thanksgiving Day White House news conference that Shultz and Gromyko will not delve into the substance of arms control issues but will focus on achieving "a common understanding as to the subject and objectives of such negotiations."

The Shultz-Gromyko meeting, as described by McFarlane, appears to be regarded by the administration as a first step toward a possible full-scale new start on the arms talks that have been in limbo since late last year. Left unclear by yesterday's announcement was how the two nations intend to bridge their sharply different views on what issues to negotiate.

The Soviets want to give priority to stopping development of weapons in space. The United States has been reluctant to consider agreements in that area and has put its emphasis on reduction of intercontinental and medium-range nuclear missiles. The tone of statements made here and in Moscow yesterday indicated that the two sides still have a long way to go in their search for sufficient common ground for substantive negotiations.

McFarlane said the agreement, which evolved from discussions between the two sides over the past several weeks, is in line with Reagan's proposal for "umbrella talks that will encompass the full family of issues" in U.S.-Soviet relations. However, the emphasis in Geneva will be on what McFarlane called "the most pressing" issues -- strategic nuclear weapons, intermediate-range nuclear weapons and outer space weaponry.

In Moscow, Lomeiko said that the two governments are talking about "completely new negotiations." He said the Soviet Union does not regard the Shultz-Gromyko meeting as a continuation of the parallel Geneva talks on limiting strategic and intermediate-range nuclear missiles that were suspended by the Soviets a year ago after the United States began deploying medium-range cruise and Pershing II missiles in Western Europe.

Lomeiko said the Soviet Union still insists that the suspended talks cannot resume until the United States and its North Atlantic Treaty Organization allies remove the missiles, which are capable of striking deep into Soviet territory from their West European sites.

McFarlane turned aside as "premature" questions about whether the suspended Geneva talks will be put back on track or whether Shultz and Gromyko will agree on some way of picking up the negotiating threads in these two areas.

He said the purpose of the January Shultz-Gromyko meeting and "possible follow-on meetings" is to discuss "scope, venue and timing" for negotiating the three sets of issues.

Although McFarlane indicated that the United States sees advantages in using the formats that had been established by the suspended Geneva talks, he added, "We are ready to talk and listen to alternative ideas on the other side."

The important thing, he said, is that yesterday's announcement "does confirm that the Soviet Union does intend to negotiate toward agreements on nuclear arms, and they have so stated in the announcement . . . . It is essential that there be a sustained effort. We don't say that this is a milestone of conclusion, but a beginning."

McFarlane also sought to give a big share of the credit for yesterday's development to Reagan, whose stress on negotiating from a position of strength led critics to charge that he is not really interested in reaching arms control agreements.

McFarlane said he advised the president on Monday in Santa Barbara, Calif., that a tentative agreement had been reached. He quoted the president as saying:

"This is good news. It is the first step on what will be a long and difficult road. But the world is depending on us. I want you to get back to Washington and speed up the work necessary to prepare our position."

The agreement came after a long chill in U.S.-Soviet relations, punctuated by the Soviet walkout from the Geneva negotiations last year and the lack of an accord on a Soviet proposal to meet last September in Vienna to discuss space weaponry. That idea foundered after the Soviets charged that the U.S. desire to bring up other issues in Vienna, such as resumed missile talks, was an attempt to attach unacceptable preconditions.

McFarlane, citing the need to keep diplomatic exchanges confidential, refused to give a detailed account of how the stalemate was broken.

He did say that the process began when Reagan unveiled the idea of umbrella talks in a September speech to the U.N. General Assembly and in a subsequent White House meeting with Gromyko.

That, McFarlane said, was followed by a lengthy period of exchanges at various levels in which the two sides sought to gauge each other's views more closely. Following his Nov. 6 reelection, Reagan sent a message to Soviet President Konstantin U. Chernenko, expressing his commitment to improved relations and arms reductions in his second term.

Then, last Saturday, a Soviet message, reportedly signed by Chernenko, informed Washington of Moscow's willingness to have Shultz and Gromyko meet to work out details of a resumed superpower dialogue.

McFarlane said, "The appreciation on both sides of each other's thinking has matured to the point where both sides think it timely to engage in talks."

McFarlane also was asked about persistent speculation that Reagan might appoint an "arms control czar" or "special envoy" to oversee the entire arms control agenda.

"The public portrayal of that idea has been of a person who would oversee the decision process here and also participate in the negotiations. There are no plans to appoint such a person," McFarlane said.

Instead, McFarlane said he will act as general coordinator of all U.S. arms control planning under Reagan's close direction.

But, in response to questions about a "special envoy" whose mandate would be more circumscribed, he said, "There is possible value in having someone -- once talks are under way -- to advise, to troubleshoot and to be a designated hitter to ensure that momentum is sustained over time. There has been no decision about that. But a distinction should be made between someone who does that and someone who manages the process here in Washington."

Asked whether the agreement has made a summit meeting between Reagan and Chernenko more likely, McFarlane noted that Reagan has said on several occasions that he would be willing to meet the Soviet leader if the meeting was well prepared and showed promise of tangible results.

But, McFarlane added, it is "very premature to speculate" about whether the Shultz-Gromyko meeting might lead to a summit.