Soviet leader Leonid I. Brezhnev's prodding criticism of the Carter administration yesterday on nuclear arms control negotiations coincides with intensive planning by U.S. strategists for talks in Moscow on April 20-21.

The timing appeared to be quite deliberate. Both nations are putting a high stake on this month's negotiations, in which Secretary of State Cyprus R. Vanve will lead a delegation to the Kremlin for the second time in the Carter administration. Their first encounter, in March 1977, ended in deadlock that took months to overcome.

Adninistration spokesmen offered no immediate official comment on the Brezhnev speech, which broke no new ground and continued Sovier claims that the United States is dragging its feet on completing the long-delayed strategic arms limitation talks (SALT).

The Brezhnev speech, in tone and in setting, was virtually a response to President Carter's stern speech at Wake Forest University in Winston-Salem, N.C., on March 17, before Carter boarded the nuclear-engined aircraft carrier Eisenhower for a display of American military power.

Carter in that speech warned against an "excessive Soviet buildup" of military forces. He also described the Soviet projection of "proxy forces" into distant conflicts (meaning the use of Cuban troops in the Horn of Africa) as an "ominous" sign, and said he will assure that a new SALT agreement "preserves the strategic balance.

Administration leaders are now engaged in intensive preparations for the new Moscow round of nuclear bargaining.

Vance, Defense Secretary Harold Brown and presidential national security affairs adviser Zbigniew Brzezinski had lunch yesterday at the State Department. Later, at the Pentagon, Vance and Brown met with the Joint Chiefs of Staff on negotiating strategy for the Moscow nuclear talks.

Consulations on SALT will continue at the White House early next week, as both Vance and Brown will be abroad suring the days immediately oreceding the Moscow talks.

Brown is leaving Washington Tuesday night for western Europe, on a trip that concludes in Copenhagen for a meeting of the North Atlantic Treaty Organization's nuclear planning group.

Vance is scheduled to leave Washington on Thursday on an exhausting schedule of travel to Africa, from which he just returned with Carter, and then on to Europe.

With arrangements still subject to change, Vance plans to meet in Arusha, Tanzania, April 15-16 with British Foreigh Secretary David Owen and leaders of the Patriotic Front, which is conducting guerrilla warfare against Rhodesia.

On April 17, Vance is scheduled to make the first visit of an American secretary of state to Salisbury, Rhodesia. There he plans to meet with the leadership of the interim government. Prime Minister Ian D. Smith and the three moderate black leaders of the so-called internal nationalist factions.

Next Vance is scheduled to go to London April 18 for the annual meetting of the Central Treaty Organization (Britain, Iran, Turkey, Pakistan, United States) originally scheduled here April 19-20.

From LOndon Vance is due to travel to Moscow, on April 19, for the strategic nuclear negotiations April 20-21, which may continue into another day.

If the agreement has been reached between the external and internal Rhodesia factions for the projected "all-parties" meeting, about April 24, to try to avert a black-black civil war, Vance would attend that conference after Moscow. Even the site of that meeting is uncertain, with Geneva, Malta and other locales mentioned.