The Carter administration has imposed a moratorium on most high-level official trips to the Soviet Union because of the trials of dissidents and other recent Soviet actions, and at the same time has approved new official missions to Moscow's arch-rival, the People's Republic of China.

Government sources [WORD ILLEGIBLE] conflicting renditions of the relationship of the two lines of actionin the exchange field, some officials denying and some affirming that the China decisions were part of [WORD ILLEGIBLE] U.S. reaction to developments in Moscow.

There was no doubt, however, that the U.S. actions will place new strain on the unusually tense and acrimonious relations with the Soviets. Officials expressed hope but no certainty that the suspension of missions to Moscow will serve as a warning that new steps toward harsh treatment of Soviet dissidents. American businessmen and journalists could bring about stronger U.S. countersteps and a continued worsening of the political relations between the superpowers.

The deferral of high-level trips "as a general rule" due to concern about developments in the Soviet Union was announced by State Department spokesman Hodding Carter in response to questions about the cancellation of a planned visit to Moscow" by Lawrence B. Simons, assistant housing and urban development secretary and federal housing commissioner. His was the third such cancellation this month of a government mission to the Soviet capital.

Holding Carter said the policy would be applied on a "cease-by-cease" basis and indicated that trips concerning arms control efforts with Soviets would not be affected.

"As we perceive a better atmosphere on various issues affecting our relationship, we would allow exchanges once again to become more active," Carter said.

The trips to China that have recently been approved include a mission to be headed by Secretary of Energy James R. Schlesinger Jr., according to infromed sources. Schlesinger visited China for three weeks in September 1976, as a private citizen and ex-secretary of defense, in a trip that took him to sensitive areas of the Sino-Soviet frontier and featured extensive discussions of military affairs.

His upsoming trip is being described in official quarters as the return visit for the tour of the United States earlier this year by Chinese petroleum and energy experts. The energy secretary served as host for this group. However, his strong views about the Soviet Union and his growing role as a participant in Carter administration decision-making on strategic and nuclear matters are expected to ensure a warm welcome from the Chinese and special concern on the part of the Russians.

In addition to Schlesinger's trip, other official exchanges with China are in the works following the recent five-day trip by White House science adviser Frank Press and 12 top scientists in the Carter administration. A subsequent visit to Moscow by Press and a delegation of scientists was canceled after the Soviet dissident trails.

An administration official concerned with U.S. reaction to developments in the Soviet Union describedthe deferral of trips to Moscow as a "tactical" action due to special circumtances and described the increase in trips to China as a separate "strategic" measure concerning overall policy toward Peking.

Another administration official, however, depicted the Schlesinger trip as an additional message to Moscow devised by presidential assistant Zbigniew Brzezinski.

The first cancellation of an official mission to the Soviet Union, that of Deputy Administrator Barbara Blum of the Environmental Protection Agency, was ordered by Secretary of State Cyrus R. Vance July 7 following announcement of the Kremlin decision to try Anatoly Scharansky and Alexander Ginzberg. Vance extended the policy to other Moscow missions of U.S. policymaking personnel, according to informed sources. However, no announcement of the general policy was made until yesterday.

Aides to Transportation Secretary Brock Adams said yesterday he has canceled plans to visit Moscow in September to sign an agreement on the exchange of transportation technology.

Decisions that could be affected by the policy in the next few weeks, in the absence of improved relations, include the planned participation by policymaking officials this fall in U.S.-Soviet commissions on transportation, health, energy, environment and oceans. The commissions are among the symbols and benefits of detente that originated in the Nixon administration.