While the new U.S. administration studies defense budgets and Caribbean military scenarios, the Soviet Union has been effectively building a potential military threat to southern Europe and to U.S. Mediterranean sea and air communications in Libya.

More than 5,000 Eastern Bloc military and civilian personnel, including Cubans, and an immense $12 billion arsenal of mainly Soviet weapons are in Libya, according to senior U.S. and allied intelligence sources.

Col. Muammar Qaddafi, the Libyan leader, repeatedly insists that the Soviet military presence exerts no political influence on his decisions.

Stung by Western suggestions that the Kremlin had helped instigate his recent military invasion and virtual annexation of Chad, Qaddafi said in a speech purely a Libyan responsibility and neither the Soviet Union nor any of our other friends bear responsibility for this action."

Since his first big arms deal with the Soviets in 1974, Qaddafi has sold Eastern European states and Soviet satellites oil on favorable terms, thus easing the Soviet obligation to supply them. At the same time, Qaddafi's strategy of combating U.S. and Western European, including French, influence in the Third World, also suits the Kremlin.

Western petrodollars paid for Libyan oil are to fund massive Soviet arms purchases. Through this, Qaddafi is helping the Soviet Union to become "a Mediterranean power" on Western Europe's back doorstep, as the Soviet Navy commander-in-chief, Adm. Sergei Gorshkov, said it would do in 1972. That was the year Egyptian President Anwar Sadat expelled Soviet ground, air and naval forces from Egypt.

The Soviet-Bloc military and civilian personnel serving in Libya provide logistical support and maintenance for Qaddafi's 7,000-member Army contingents and mixed "Islamic legion" force of Libyan-trained Arabs and Africans in Chad. Of even greater long-range concern to U.S. and allied military planners, however, are the vast stores of Soviet jet aircraft, tanks, artillery and short- and medium-range missiles positioned in Libya, close to main U.S. sea and air communications lines toward the Middle East and Persian Gulf, and less than 300 miles from Italy and Greece.

In his March 2 speech, Qaddafi reiterated that "almost all of our weapons are supplied by the Soviet Union. The Soviet Union gave us the most dangerous and the most modern weapons; we bought them from the Soviet Union, wheareas the United States, with our own money and funds, refuses to sell us even civilian cars." The United States has embargoed truck and cargo plane sales because of Libyan support for terrorism. e

Clearly eager to defend himself against charges by Saudi Arabians, Tunisians and other Arabs and Africans that Libya is becoming a "Soviet base," Qaddafi recalled that "from the revolution [1969] until now, we have not permitted naval warships either of the United States or Russia to enter Libyan territorial waters."

Senior U.S. analysts agree that Qaddafi has not allowed the Soviets to use Libya's ports or airfields, although allied intelligence has been closely watching for signs that Qaddafi's closure last December of Benghazi's big international airport to foreign civil air traffic could presage this.

Between 1,000 and 2,000 Soviet military personnel, controlled by Soviet staff officers installed in the Soviet Embassy compound in Tripoli, form the elite of the instructors and advisers. They operate down to rigimental and sometimes battalion level, training and helping maintain tanks, rocket launchers, artillery and aircraft. Some are believed to advise the Libyan general staff.

Between 600 and 1,000 Cubans wearing civilian clothes perform these tasks and also many civilian ones, including road building and construction.

From 1,500 to 2,000 East Germans, coming from the same "new wehrmacht" already identified in Ethiopia, South Yemen, Mozambique and other Eastward-learning Third World Countries, direct and guide Qaddafi's intelligence and security services.

Their principal specialties are signal intelligence and electronic eavesdropping, as once taught to Libyans by ex-CIA officer Frank Terpil, who slipped away after his arraignment in Washington on arms-traffic charges last summer and is now believed back in Libya with several other American and European "contract" workers for Qaddafi.

East Germans, say sources recently in Libya, also staff Qaddafi's body-guard and provide the physical security for his well-fortified, partially underground Bab Azziziya headquarters at the gates of Tripoli.

It was East Germans, say European experts on Libya, who were probably decisive in putting down an Army mutiny in the Tobruk area last August. A brigade-sized unit tried to trigger a revolt whose leaders, if successful, would have called for help from Qaddafi's main adversary and neighbor, President Answar Sadat of Egypt, who has vowed to fight if Libya invades Egypt's giant but impoverished neighbor, Sudan.

Qaddafi's Soviet-built jets were active in the successful Libyan expedition into Chad in support of provisional Chadian President Goukouni Oueddei last November and December. They are not believed to have fired any of the larger air-to-ground projectiles.

A small contingent of North Korean Air Force personnel, comparable in size and function to the 20 or so that quietly served Egypt before and during the 1973 war, now operates in Libya. Some are pilots or in charge of pilot training, but it was Syrian and possibly one or two Pakistani and Palestinian pilots, flying Libyan Migs, who challenged and nearly clashed with U.S. Navy reconnaissance planes and their fighter escorts from the U.S. 6th Fleet several times over the Gulf of Sidra last year.

Libya's Air Force of 200 combat planes, the best in North Africa, has come a long way from the tiny force of 15 or so pilots flying U.S.-supplied Northrop F5s and Lockheed C130s when Qaddafi took power.

However, the Air Force has not been without its internal troubles and defections.One Mig23 crashed in Sicily last July in an apparent attempt by its pilot, who was killed, to reach a NATO air base.

On Feb. 11, another Libyan pilot flew another Mig23 to the Greek-American and NATO air base at Suda Bay, Crete. He landed successfully, but slightly damaged the plane. Greece returned it disassembled and granted the pilot political asylum.

The Greek Foreign Ministry denied Greek newspaper reports that Libya had threatened to cancel lucrative oil and construction deals with Greek contractors (including one for a military target range), or to impound Greek shipping in Libyan waters, if the pilot was not returned. However, one Greek fishing trawler was seized in Benghazi harbor.

The first and only Soviet naval visit to Libya took place in May 1969, while King Idris still ruled and Qaddafi, then an unknown lieutenant of the Libyan signal corps, was still plotting his Sept. 1 coup. A Mirka-class Soviet frigate entered Tripoli harbor, ostensibly for emergency repairs. It left, after apparently taking the opportunity to inspect newly arrived British-made Libyan naval craft.

In early 1975, 100 Libyan naval personnel began four-year submarine training in the Soviet Union in connection with Soviet supply of at least four 2,000-ton diesel submarines, since delivered to Libya.

Libyan sources say Qaddafi has prepared heavily fortified underground bunkers, both at Bab Azziziya in Tripoli and at Sirte, a few miles north of an apparent new capital being built at Jefra.

These, a private airstrip with an executive jet and a submarine fitted out in Italy as an underwater command post in case of revolt or war are heavily defended. Missiles in place in Sirte, says a Libyan former diplomat, Mohammed Mugareiff, are pointed at both Tripoli and Benghazi, in case forces hostile to Qaddafi should seize control there.

Qaddafi, said another Libyan formerly close to the leader, "has gambled in a big way on the Soviets. They think they are usingt him, and he is sure that he is them. Both of them are right." CAPTION: Picture, Muammer Qaddafi: Host to 5,000 Eastern Bloc troops and their $12 billion arsenal. Sygma