Ambassador Paul H. Nitze has been given an office close to that of Secretary of State George P. Shultz in a symbolic move that officials said presages a key role in future arms control negotiations with the Soviet Union.

His shift to the State Department's seventh floor reflects a desire "to plug Paul in" to the preparations for the forthcoming meeting in Geneva between Shultz and Soviet Foreign Minister Andrei A. Gromyko and means that the veteran negotiator is likely to accompany Shultz, an informed administration source said last night.

Nitze, 77, was chief U.S. negotiator with the Soviets in unsuccessful 1981-83 negotiations on limitation of medium-range nuclear weapons in Europe. He is the most experienced U.S. negotiator with the Soviet Union now active.

A conservative on defense matters who was the intellectual leader of the opposition to the 1979 SALT II treaty, he is nonetheless considered a "problem-solver."

Officials said it is unlikely that Nitze will be formally named at this time to head a team in bargaining that Washington and Moscow hope will flow from the Shultz-Gromyko meeting.

However, the officials said they now expect Nitze to have a central negotiating role under the overall supervision of the president and secretary of state.

"We don't know for sure what his job will be until after" Shultz meets with Gromyko on Jan. 7-8, said an official. This is because nobody is certain how far the two foreign ministers will proceed, or what the decision will be, in structuring future U.S.-Soviet negotiations involving a range of complicated issues: weapons in space as well as offensive strategic arms and medium-range weapons in Europe.

President Reagan, in his September meeting with Gromyko, suggested that each country name a "special envoy" to try to break the stalemate. There has been no Soviet response but U.S. officials plan to explore the idea in Geneva.

Nitze will also retain his present office at the Arms Control and Disarmament Agency, in effect wearing two hats until the outcome of the Shultz-Gromyko session, officials said.

In a related matter, Assistant Secretary of State Richard R. Burt said yesterday that it would be "very difficult for any U.S. president to get a treaty ratified" by the Senate unless concerns over Moscow's past arms-agreement violations are "cleared up."

Burt also said he agreed that "there should be penalties" for the Soviet Union when the United States determines there have been violations. But he added, during a question period at an American Enterprise Institute meeting, that "it is a difficult area to deal with."

Meanwhile, conservative members of Congress continued to pressure the White House on the issue of violations. Republican Sens. Stephen D. Symms (Idaho) and John P. East (N.C.) wrote the president that they might not support funds for the MX missile if he continues to abide by the SALT II treaty.

The two senators accused the government of "appeasing" the Russians, who they said were not living up to the SALT II commitments.

The Arms Control and Disarmament Agency has begun studying what steps could be taken, short of withdrawing from the agreements, in cases where the United States determines Soviet violations, an agency official said yesterday.