Ambassador Paul H. Nitze, special adviser to the president and secretary of state on arms control, said yesterday it will take "at least 10 years" to determine whether a new space-based defense against Soviet ballistic missiles is possible.

It will take a decade of research to find out whether such a defense, the goal of President Reagan's Strategic Defense Initiative, would "meet the criteria of being survivable and cost-effective," Nitze told a gathering of constituents of Rep. Timothy E. Wirth (D-Colo.)

Previously, administration officials had talked more vaguely of research over five to 10 years before a determination on the practicality of the so-called "Star Wars" system could be made. But Nitze said yesterday that it would be 10 years or longer before the United States would be prepared to "negotiate with the Soviet Union ways and means such a system could be introduced."

Nitze was referring to the fact that a space-based defense could be introduced only if the terms of the existing Anti-Ballistic Missile (ABM) Treaty are amended or abandoned.

Speaking to the same meeting, Assistant Secretary of Defense Richard N. Perle said the United States should be prepared to violate existing arms control agreements if the Soviets continue to violate them. "Continued unquestioned adherence" to agreements in the face of Soviet violations will produce an "unwise . . . double standard," Perle said.

Perle's statement echoed a Pentagon report to Congress last week that said the United States might respond to Soviet treaty violations with some of its own. Using similar language to Perle's yesterday, the Pentagon said the U.S. government "must guard against permitting a double standard of compliance, under which the Soviet government would expect to get away with various violations of arms agreements while the U.S. continues to abide with all provisions."

Perle made his observations in responding to a question on whether the United States would continue to adhere to the unratified SALT II treaty this fall, when a new Trident submarine with 24 missiles is scheduled to be sent to sea. That sub will put the U.S. total of deployed multi-warhead missiles above the SALT II limit for such systems.

"No decision has been made" on whether to reduce other systems to stay within the limit, Perle said.

He went on to say, however, that it was "a peculiarity of Americans" that to demonstrate good faith, "we should abide by a treaty that they the Soviets are violating."

He said it is "worth waiting" for an agreement with the Soviets that would bring about substantial reductions in their missile force rather than "an agreement that permits them to keep programs that they plan to do anyway."

"I'm not troubled that there is not an arms control agreement around the corner," Perle said.

Both administration officials raised the issue of the Soviet radar in central Siberia near the town of Krasnoyarsk that the president has termed a violation of the 1972 ABM treaty.

Nitze said the radar closes a gap in the Soviet early-warning coverage. He added that if the Soviets had followed the treaty language requiring such facilities to be placed on the perimeter of the country, "they would have had to build two . . . in tundra" and "they would be very difficult" to maintain.

"It's perfectly clear why they have done this," Nitze said of the violation.

Perle, noting that Soviet violations of arms agreements normally is "glossed over," said, "I welcome this violation" because it had opened up the subject of compliance for public discussion.