In one of a series of U.S. moves of concern to the Soviet Union, Secretary of State Cyrus R. Vance has begun planning a trip later this year to Yugoslavia and Romania, two sensitive and independent-minded nations on Russia's periphery.

Administration officials took pains yesterday to say that the trip, planned as an extension of Vance's mid-December journey to the North Atlantic Treaty Organization ministerial meeting in Brussels, is unconnected with Washington's continuing displeasure over the presence of a Soviet "combat brigade" in Cuba.

The Russians, however, are known to be apprehensive that this and several other newly revealed steps are part of a "tit-for-tat" drive to make them uncomfortable in their own sphere of influence.

Such a drive was hinted at by President Carter and national security affairs adviser Zbigniew Brzezinski in public statements while the troops-in-Cuba issue was under negotiation with the Soviets.

On Sept. 7, Carter declared that "we do have the right to insist that the Soviet Union respect our interests and our concerns if the Soviet Union expects us to respect their sensibilities and their concerns." Brzezinski on several occasions referred to a "principle of reciprocity" as a factor in U.S. action toward the Russians if the troops issue could not be settled through diplomatic means.

In the wake of Carter's report to the nation Monday night, several American officials denied that unannounced anti-Soviet countermeasures had been adopted by the president in retaliation for Moscow's refusal to cooperate on the troops issue. Some officials suggested that a number of such measures had been considered but rejected in high policy councils.

Since the beginning of this week, however, several steps have come to light by design or coincidence that are worrisome to the Russians:

News of Defense Secretary Harold Brown's forthcoming trip to the people's Republic of China, the arch-enemy of the Soviet Union, was leaked to Newsweek and The Wall Street Journal. This first-ever visit by a Pentagon chief to communist China fuels speculation about future U.S.-China military cooperation.

A copy of a Pentagon contingency study, "Consolidated Guidance No. 8: Asia During a Worldwide Conventional War," was leaked to The New York Times. The study suggested building up China's military potential through such things as arms sales and intelligence exchanges in order to weaken the Soviet Union in case of war.

The proposed upgrading of an American computer in use outside Moscow will be vetoed on the advice of the Pentagon, reporters were told. Officials said that before the troops-in-Cuba issue, a task force including the Defense Department had gone along with shipment of additional equipment to Russia to upgrade the Cyber 73-1 computer.

Offsetting such news, and welcome to the Russians, was the announcement Wednesday by the Department of Agriculture that in the coming year the United States will sell up to 25 million metric tons of wheat and corn to the Soviet Union, the largest grain purchase in history. Some administration officials in the foreign policy field were very unhappy with the grain announcement, the timing of which apparently was dictated by a prearranged set of negotiations with the Soviets and by the beginning of a new U.S. crop year last Monday.

State Department spokesman Hodding Carter defended the grain sale yesterday, saying it will be "mutually beneficial" to the United States and the Soviet Union.

Those who criticize such a deal because of the troops issue reminded Carter of some who might suggest amputating an arm "just to get rid of a wart on a finger" or cutting off an ear to get rid of a bug.

Officials who maintain that no pattern of "get tough" actions toward the Russians has been adopted are ready with explanations for all the new items that are worrisome to Moscow.

Vance's foray into Eastern Europe has been under discussion and consideration for months, officials said, although near-final decisions have been taken only in the past several days. While denying that the journey is a signal to the Soviets regarding U.S. ire about Cuba, the sources said it is a signal of U.S. support for the independence of Romania and Yugoslavia. Vance has not been to either nation previously as secretary of state.

The Brown trip to Peking, according to administration officials, was discussed within the White House in April, recommended to the president in July and approved before Vice President Mondale tried it out on the Chinese in his August trip to Peking. All this was before the emergence of the Cuba troops issue.

Some sources said -- and others denied -- that announcement of Brown's China trip was considered and rejected as an anti-Soviet option in the decision making that led up to Carter's address Monday.

Any presidential decision on this point was made moot by the well-timed news lead, whether authorized or unauthorized.

As for "Consolidated Guidance No. 8," Vance went out of his way yesterday to state "flatly and categorically" that the United States has no intention of changing its policy against arms sales to China. Pentagon spokesman Thomas Ross called the 1978 study "primarily a think piece" that does not represent U.S. policy.

Vance also denied that the computer decision was related to the Soviet troops issue. An advocate of parallel U.S. relations with the rival giants of world communism, Vance said items of potential military value are usually withheld from Moscow and Peking alike.