The prime minister of Mauritius said today that he will try to make the U.S. military base on Diego Garcia Island a major issue at the seventh summit of the Nonaligned Movement here next month.

Prime Minister Aneerood Jugnauth also said that he will continue to press Britain for Mauritian sovereignty over the island--which Britain leases to the United States--and that he will not yield on his vow to ban U.S. and Soviet warships from calling on Mauritius because of the continued U.S. use of Diego Garcia as a strategic staging base.

At a press conference after a two-day official visit here, Jugnauth said the loss of needed foreign exchange from the ban had been considered but was "secondary" to the principle involved in Diego Garcia, which is 1,174 miles from Mauritius.

Attempts by the United States and the Soviet Union to fill the power vacuum in the Indian Ocean since the departure of the British fleet have become a major issue for India and others of the 36 nations in the region. Britain separated the archipelago including Diego Garcia from Mauritius in 1965 as part of an agreement that led to Mauritian independence three years later. The island nation remains in the Commonwealth.

Jugnauth, a socialist, said he had discussed the issue with British Prime Minister Margaret Thatcher, who said that the U.S. base was necessary for the West's defenses but that Mauritian sovereignty could be considered when the base was no longer a strategic imperative.

The United States, which leased Diego Garcia for 50 years, has made the tiny coral atoll a hub of its Rapid Deployment Force, investing nearly $1 billion to lengthen runways to handle B52 bombers, improving port facilities to accommodate U.S. carrier-led battle groups, and building warehouses to store military equipment that could be used in the event of a Persian Gulf crisis.