SYDNEY, JUNE 22 -- The United States and Australia, determined to check increasing Soviet activity in the South Pacific, declared today that their alliance was strong and effective despite continuing friction over U.S. trade policy and French nuclear tests.

Secretary of State George P. Shultz and Defense Secretary Caspar W. Weinberger agreed with their Australian counterparts, Foreign Minister Bill Hayden and Defense Minister Kim Beazley, in a daylong series of meetings that they must respond to the Soviet Union's increasing commercial and diplomatic activity among the tiny island nations of the South Pacific.

"We can assume that the Soviet Union will go on taking diplomatic, commercial, intelligence and other initiatives in the region aimed in part at undercutting vital alliance interests in the Pacific," Shultz said.

Hayden, who said Moscow was acting through regional "front organizations" as well as its own fishing fleets and other ventures, said the island nations lacked the police and intelligence resources to contain the threat on their own.

Shultz is scheduled to leave Australia Tuesday and will stop in Western Samoa on his way home in a five-hour visit intended to dramatize U.S. concern over Soviet and Libyan penetration of the region.

Today's meeting was billed as the annual conference of the ANZUS (Australia, New Zealand, United States) alliance. The membership of New Zealand has been suspended because it refused to permit U.S. nuclear-armed and nuclear-powered warships to visit its ports, but the United States and Australia declared that their alliance "remained constant and undiminished" despite its loss.

Australia, angry about U.S. subsidies of agricultural exports, insisted on inserting into the final statement an implied warning that it might reduce its commitment to the alliance. "The Australian side stressed that protectionism and agricultural subsidies in the major world markets distorted the earnings of efficient primary commodity suppliers," the statement said. "To the degree that this imposed economic strains on Australia, it impaired Australia's ability to work effectively in cooperation with its allies and friends."