The United States has began "exploratory discussions" with allied nations about the possibility of joint naval action in case of a threat to shipping traffic through the critical Strait of Hormuz in the Persian Gulf, the Pentagon said yesterday.

Spokesman Thomas B. Ross, In confirming the talks, said, "No decisions have been made on a multinational task force or other joint activities."

Defense sources said the talk began late last week between U.S. Navy officials in Washington and naval attaches here representing Britain, France, Italy, Australia and New Zealand.

The naval discussions, which were described by officials as contingency planning, followed political-level exploration of the idea of joint naval action last week in New York by Secretary of State Edmund S. Muskie and foreign ministers of several of the allied nations.

An interruption of traffic in the strait of Hormuz, the potential choke-point in the "world oil highway" that is the Persian Gulf, seems less likely today than it did earlier in the 11-day-old Iraq-Iran war, officials here said. Iran Wednesday, issued a formal statement declaring that it will keep the strait open "in full view" of its "international obligations."

In view of the vital importance of the international oil flow through the strait, however, the idea of joint planning to respond to an emergency has gained favor with several nations, but hardly any nation is anxious to say much about it in public. Action on a multinational basis is believed more likely to be palatable politically in the gulf area than action by the United States along.

The United States is keeping two aircraft carrier task forces near the Persian Gulf, according to defense officials. The task forces, headed by the carriers Midway and Eisenhower, can launch about 170 aircraft, a significant tactical force.The United States has 31 ships in the area.

According to defense sources, France has a 15-ship force, in Middle Eastern and East African waters. A British destoryer, accompanied by an oiler, is heading to the Indian Ocean. Australia has an aircraft carrier and its destroyer escorts headed toward the area on a mission scheduled before the Iraq-Iran war broke out.