West Germany "is secretly testing the cruise missile" with U.S. approval on a huge test side it has leased in Zaire, Penthouse magazine reported yesterday.

The Central Intelligence Agency, Defense and State departments all denied any involvement with a German firm's space activities in Zaire, while the West German embassy said no cruise missile testing was going on there.

The Soviet Union last August formally protested to the Boon government the alleged West German military base in Zaire Bonn responded then that the activity consisted of a private German firm trying to develop a cheap rocket for launching weather satellites.

"With the knowledge and approval of the United States," said the Penthouse article by former New York Times diploinatic correspondent Tad Szule, "West Germany is secretly testing the cruise missile - potentially the most deadly weapon of the nuclear age - and the intermediate range ballistic missile (IRBM)" on 100,000 square miles it has leased from Zaire for $50 million a year.

Penthouse said a German firm called Orbital Launch and Rocket Corp. (OTRAG) leased the tract March 26, 1976, for 24 years. As quoted by the magazine, the firm's contract with Zaire gives OTRAG "the right to take all measures that it deems necessary for the exercise of full and complete power in the territory . . ."

Developing missiles in Zaire, Penthouse said, would circumvent the 1954 Treaty of Brussels designed to prevent unlimited rearming of Germany. That treaty forbids the development of missiles inside West Germany. "Carter administration officials have privately confirmed," said the article, that the CIA and its West German counterpart have helped recruit "American trained" Scientists for the rocket program in Zaire.

Said the CIA when queried on the article: "We deny the CIA is involved in any way."

Defense officials said their department has no involvement with the German facility in Zaire.