Government officials disclosed yesterday that Cuba has reinforced its expeditionary force in Angola during the last few weeks, underscoring the administration's view of the need for the new U.S.-Israeli agreement to combat Soviet surrogates threatening the Middle East and Africa.

The Cuban contingent was reduced from about 12,000 troops to 10,000 during South African raids into Angola in September, the officials said, but is now back up to between 12,000 and 15,000.

One U.S. theory holds that Cuban President Fidel Castro decreased his forces at the very time Angola was under attack in order to underscore his warning that Cuban forces should not be taken for granted by host nations.

Also, sources said, Angola was behind in its payments to Cuba for military help. Angolan officials have told foreign diplomats that Cuba charges $40 per day per soldier.

Besides the Cubans in Angola, according to U.S. intelligence estimates, Castro still has about 12,000 troops in Ethiopia and 600 in South Yemen.

Pentagon spokesman Henry E. Catto Jr. said yesterday that Cuba and East Germany were nations the United States and Israel had in mind when they pledged in a memorandum of understanding signed Monday to work together against threats from "Soviet-controlled forces from outside the region introduced into the region."

Other U.S. sources said yesterday that hundreds of highly skilled East German military specialists are operating in Algeria, Libya, Mozambique, South Yemen and Zambia. "They're awfully good," said one official in crediting them with accomplishments larger than their small numbers would suggest.

Although the United States and Israel are plainly worried about these Soviet surrogates from Cuba and East Germany, military planners freely admit they have no fresh plans to deal with them directly. The more attractive option from a military viewpoint is to punish Cuba at home for trouble its troops cause abroad.

Although the U.S. Rapid Deployment Force is designed to respond to trouble in the Middle East, its contingency planning has focused on combating Soviet thrusts against oil fields in Saudi Arabia and Iran, not internal subversion by Cubans or East Germans in the region.

The Israelis, sources said yesterday, wanted to go much farther in military cooperation with the United States than the landmark memorandum of understanding provides.

Israel's suggestions, they said, ran to several pages and included elaborate joint logistical arrangements, not just such previously mentioned proposals as storing U.S. weaponry in Israel and repairing U.S. warplanes at bases there.

Israeli Defense Minister Ariel Sharon went home yesterday with little of what he had requested, officials said. This may explain why the administration held no briefing on the new strategic agreement and conducted its signing Monday night at a dinner at the National Geographic Society building with no press admitted.

Catto denied that he had told defense officials not to discuss the agreement with the media. He said "the understanding" from the outset was that Defense Secretary Caspar W. Weinberger and Sharon would sign the memorandum of understanding privately.