The United States and the Soviet Union are close to a "sustainable" long-term relationship as a result of three summit meetings in three years and key shifts within both nations, Secretary of State George P. Shultz said yesterday in a major policy statement.

"On the U.S. side, there is for the first time in many years a consensus on how we should deal with the Soviet Union," said Shultz, citing widespread public acceptance of a broad U.S.-Soviet agenda and of the necessity for dialogue.

"On the Soviet side, there may be -- for the first time ever, and as a result of necessity -- a willingness to reexamine Soviet security and other interests in ways that are closer to international norms," he declared in a speech prepared for delivery to the Henry M. Jackson School of International Studies at the University of Washington in Seattle. The text was made public at the State Department.

Asserting that the Reagan administration has implemented a policy "flexible and resilient enough to adapt to changing circumstances," Shultz maintained that the United States is now "well positioned to deal with the best and worst of Soviet behavior."

"The case can be made that we are near a threshold of a sustainable U.S.-Soviet relationship," he said.

Shultz essentially repeated from his last broad U.S.-Soviet address, delivered in Los Angeles in October 1984, the main lines of policy toward the Soviet Union. They include the necessity of strength and dialogue in dealing with Moscow and opposition to the concept of "linking" progress in arms-control negotiations to Soviet performance on other issues such as its occupation of Afghanistan and human rights.

Taking a wait-and-see stance toward Gorbachev's internal moves, Shultz said that his attempt at economic reform "is just beginning" and that structural political reform in the Soviet Union "has barely scratched the surface."

Saying there is no evidence the Soviet Union has shifted its international ambitions, Shultz said, "We must deal with the Soviet Union as it is, not as we wish it to be."

Shultz, who is scheduled to travel to Moscow in two weeks for the first of several meetings to prepare for the next Reagan-Gorbachev summit, challenged the Soviets to make "a real change of policy" in Berlin and Eastern Europe and "to put forward promptly a plan for the rapid, complete and irreversible removal of all Soviet forces" from Afghanistan by the end of this year.