Democrats on the Senate Foreign Relations Committee will meet next week to determine whether they will oppose, as a group, the nomination of Kenneth L. Adelman to head the Arms Control and Disarmament Agency, according to one Democrat on the panel.

The meeting was set, the senator said, because Adelman's performance at Thursday's confirmation hearing was considered "appalling" by several Democrats. Before that session, he said, "other than California Sen. Alan Cranston, no one had strong feelings about him on our side."

At the same time, Chairman Charles H. Percy (R-Ill.) announced that he would suspend final action on Adelman's nomination until the Reagan administration gives Percy "a date certain" by which it will deliver its final recommendations on modifying two agreements with the Soviets--the threshold test ban treaty of 1974 and the peaceful nuclear explosions treaty of 1976.

Under the treaties, the two sides agreed to limit underground nuclear explosions of weapons and peaceful devices to less than 150 kilotons, the equivalent of 150,000 tons of TNT.

Both sides have pledged to honor the agreements, although the Senate has not ratified either. Percy has been trying since early 1981 to get the administration to send the agreements up for ratification. President Reagan announced in July that he would seek amendments to strengthen the treaties' verification provisions, but those amendments have not been forthcoming.

One Senate source said yesterday that Percy "lost his patience" Thursday when Adelman said he did not know if he could get an administration decision on the treaties.

"There is no one within the administration who wants to champion either treaty," an administration official said yesterday, explaining the delay.

Meanwhile, a battle has been going on within the administration, according to sources, with one group seeking to do away with the threshold agreement in order to test higher-yield weapons, and another group wanting to improve the treaty's on-site verification provisions because they believe the Soviets are violating the kiloton limitations.

The former group, according to sources, includes Pentagon and Department of Energy officials who want the agreement to lapse so that they can test the MX missile warhead, which has a yield of more than 400 kilotons.

The warhead is based on a design that was tested before the kiloton limitation took effect.

Some nuclear scientists believe that, because of design changes, the yield cannot be certified without a new test at the warhead's full power.

State Department spokesman John Hughes said yesterday that a decision on the improvements needed to make the treaties acceptable will be ready "in the near future."

The amendments will require Soviet agreement, an official said.

Hughes also said yesterday that the United States rejected a Soviet proposal for a nuclear-free zone in central Europe, saying the idea was unrealistic and "would not contribute to security and stability in Europe."

The Soviets said the idea may be included in negotiations now taking place in Vienna.

At Adelman's confirmation hearing Thursday, Cranston described the deputy U.S. representative to the United Nations as "clearly a novice in the arms control field" and "scornful" of past arms control agreements.

But it was Adelman, 36, with vague responses to questions, who raised concern among the Democrats on the panel.

He said he had not thought about whether a limited nuclear war could occur or how he would respond if the Soviets proposed a verifiable treaty that called for the elimination of nuclear weapons.

One senator said his colleagues were "shaken" by Adelman's performance and that the television and newspaper coverage of the hearing had "set in motion an impression within the country that will be difficult to overcome."

The committee has scheduled another session with Adelman next Thursday. Members also are trying to arrange for Eugene V. Rostow, the former head of ACDA, to appear, reportedly to elaborate on the circumstances surrounding his firing two weeks ago.