The Navy, on April 25, announced it is bringing back the carrier Shangri-La from the Mediterranean, increasing to four the number of attack carriers in the vicinity of Cuba. More than 36 other big Navy ships are no less than a day's sailing time away.

To round out the blockading force, submarines would be needed -- to locate, identify and track approaching vessels. Land based radar would help with this task. So would radar picket ships. A squadron of Navy jets and another of long-range patrol planes would add support to the carrier task forces.

Three requirements go with a blockade: It must be proclaimed; the blockading force must be powerful enough to enforce it; and it must be enforced without discrimination.

Once these conditions of international law are met, countries that try to run to blockade do so at their own risk. Blockade runners can be stopped -- by gunfire, if necessary -- searched and held, at least temporarily. They could be sent to U. S. ports for rulings whether cargo should be confiscated.

Plenty, say the experts. In a broad sense, it would reaffirm the Monroe Doctrine by opposing Communist interference in the Western Hemisphere. It could, by avoiding direct intervention, provide a short-of war strategy to meet short-of war infiltration.

Primary target would be shipments of tanks, guns, aviation gasoline and ammunition coming from Russia and Czechoslovakia. Shipments of arms from Western countries could similarly be seized as contraband. In a total blockade, action could also be taken against ships bringing in chemicals, oils, textiles, and even foodstuffs. At times, three ships a day from the Soviet bloc are unloading in Cuban ports.