The White House and the State Department yesterday increased their estimate of the number of Cuban troops involved in the fighting between Ethiopia and Somalia and charged that a Soviet army general is directing Ethiopian troops in an important combat area.

At separate news briefings, Zbigniew Brzezinski, the White House national security affairs adviser, and Hodding Carter III, the State Department spokesman, both put the number of Cuban troops aiding Ethiopia at more than 10,000.

Two weeks ago, Secretary of State Cyrus R. Vance said there were 2,000 Cuban troops involved in a "combat role" in Ethiopia. Last week, the State Department increased that estimate to 5,000 troops.

At the White House, Brzezinski also asserted that Soviet Army Gen. Vasiliy I. Petrov "is in direct command" of Ethiopian troops, augmented by some Cubans, in the Harar region of the country. He said he did not know how long Petrov has been in Ethiopia.

Brzezinski also said that the Soviet Union has supplied Ethiopia with 400 tanks and 50 Mig fighter planes. The Cubans fighting on the Ethiopian side are organizing themselves into two infantry brigades and one merchanized brigade, he said.

The Soviet Union, formerly allied with Somalia, switched sides last year after the United States cut off military aid to Ethiopia.The Soviets have since poured about $800 million in military equipment in the African country.

In recent weeks, the United States has steadily increased its estimates of Soviet and Cuban involvement in the conflict. Two weeks ago, the State Department said there were 1,000 Soviets, including some pilots, in Ethiopia.

Yesterday's estimates of the number of Cuban troops varied slightly. At the State Department, spokesman Carter put it at "8,000 to 10,000 plus," while Brzezinski said there are 10,000 to 11,000 Cuban troops in Ethiopia.

The Harar region, where Petrov is said to be directing Ethiopian military operations, is part of the Ogaden, an area about the size of Oregon in abited by ethnic Somalis. Last summer, Somali forces captured most of the Ogaden from Ethiopia, which with heavy Soviet and Cuban backing is now seeking to regain the territory.

U.S. policy calls for a cease-fire in the region, followed by a negotiated settlement of the territorial dispute, the withdrawl of Somali troops from Ethiopia and the withdrawl of all Cuban and Soviet military personnel from the conflict.

Last week, President Carter publicly warned that the United States would "consider it a very serious breach of peace, endangering even worldwide peace" should Ethiopian and Soviet pledge not to escalate the war into Somalia.

Brzezinski provided the latest estimate on the number of Cuban troops involved in the conflict while answering questions about the president's planned trip to Latim America and Africa next month. One of Carter's stops will be in Nigeria.

"It is important for important countries such as Nigeria to show concern for what is a significant foreign intrusion (by Cuba) into African affairs," he said.

He said black African nations traditionally have been sensitive to intrusion into th continent's affairs, but that the situation in Ethiopia has been complicated because "the principle of territorial integrity has been violated by Somalia."

In another development yesterday, a high State Department official was quoted by Reuter as saying the United States is considering raising the Horn of Africa dispute in the U.N. Security Council.