Cuba is beefing up its anti-aircraft defenses and hosting yet another task force of Soviet warships as U.S. and Latin American officials meet in Miami today to discuss mutual problems and President Reagan's Caribbean Basin initiative.

The initiative is designed through a series of measures, many of them economic, to bring added stability and security to the region.

But the widening Soviet-Cuban military relationships provide a worrisome backdrop to those efforts, according to U.S. government authorities.

U.S. analysts focusing on the most recent Soviet military developments in the Caribbean say the United States and Soviet Union are employing updated versions of gunboat diplomacy to an increasing extent to underscore their interests in the region.

The new anti-aircraft missile site being built for Soviet SA6 Gainful weapons at Bejucal, south of Havana, was cited by analysts as part of the tightening military relationship between the Soviet and Cuban military. The Bejucal site will be the second for SA6s, sources said. The first is near Cardenas, 30 miles to the east.

The Soviet naval task force began making port calls around Cuba Thursday, officials said, and is expected to stay in the area this week.

Military analysts think the most interesting feature of the Soviet task force involves the presence of a Foxtrot diesel submarine, a Kresta cruiser, a guided missile frigate and an oiler.

The presence of the submarine may indicate, analysts said, that the Soviets intend to train the Cuban navy in anti-submarine warfare tactics for the first time.

If that is correct, it would be a leaf out of the U.S. book. The U.S. Navy for years has been practicing anti-submarine warfare with friendly navies.

Soviet and Cuban submarines could prove deadly to the United States in a wartime operation off Cuba because about 70 percent of U.S. oil traveling by ship moves through the Gulf of Mexico and Caribbean. In a Soviet-Cuban navy exercise earlier this year, analysts said, it appeared that the two navies were practicing how to defeat a blockade.

During the Cuban missile crisis of 1962, U.S. warships imposed a blockade of Cuba until offensive missiles on the island were removed.

The Reagan administration has taken several steps the last two years to give U.S. military forces a higher profile in the Caribbean. The U.S. Navy recently started sending two aircraft carriers on Caribbean exercises, the Navy has established a permanent command at Key West, Fla., to keep a closer eye on Caribbean developments and the Navy and Air Force recently agreed to conduct joint exercises off Key West in anti-ship and anti-submarine warfare.

Navy leaders do not claim that the relatively small Soviet task forces going to Cuba nor the fledgling Cuban navy could defeat the Atlantic fleet.

Rather, they contend that they do not have enough warships to cover simultaneously the Caribbean and the Atlantic, Indian and Pacific oceans.

Adm. Harry D. Train, who recently retired as commander of the Atlantic Fleet, said that if war broke out, the Soviet Union could exploit this shortage of ships by imposing a naval threat in several areas simultaneously. "The choice of the sequence may well belong to the Soviets, and we may never gain the initiative," Train said in warning Congress that the Atlantic Fleet would be trying to cover too many trouble spots at once.