President Reagan's statement to Soviet journalists that implied a sweeping change in the administration's approach to deployment of a space-based missile defense was dismissed yesterday by White House spokesman Larry Speakes as "presidential imprecision" that "the media had seized on" unfairly to suggest that Reagan had made new policy.

Reagan said that deployment of his proposed Strategic Defense Initiative (SDI) would occur only after both countries "do away with our nuclear missiles, our offensive missiles."

"We would not deploy . . . until we sit down with the other nations of the world, and those that have nuclear arsenals, and see if we cannot come to an agreement on which there will be deployment only if there is elimination of the nuclear weapons," Reagan said in the interview with four Soviet journalists that was published Monday in the Soviet Union.

Speakes said in an interview that Reagan meant to use the word "sharing" instead of "deployment" when he gave this answer.

The difference in what Reagan said and what he meant to say is significant because the president had described the SDI, frequently called "Star Wars," as a defense system that would make offensive nuclear missiles obsolete. In his new remarks, which Reagan repeated in slight variations twice more during the hour-long interview, the president suggested that he was making elimination of the offensive weapons a condition for deploying defensive weapons.

Reagan's remarks were extensively reported by newspapers, wire services and networks and caused some consternation among administration officials who were aware that the president appeared to be signaling a new negotiating position on missile defense in advance of his Nov. 19-20 Geneva summit with Soviet leader Mikhail Gorbachev. The president has repeatedly disavowed suggestions that he wants to use SDI as a "bargaining chip" with the Soviets, who want the U.S. program limited to research.

With this in mind, Speakes soon after the interview talked about what he called the "misunderstanding" to White House chief of staff Donald T. Regan, who then discussed the issue with the president. But an administration official who asked not to be identified said it was "difficult to correct the record" because no one wanted to say "that the president had misspoke."

Instead of directly correcting the president, senior White House officials tried to make an indirect correction by issuing a series of "talking points" saying that Reagan was using "presidential shorthand" when he made his remarks.

"The president was misunderstood, and he probably contributed to this misunderstanding by talking dramatically to make a point," one official said.

Late yesterday, Speakes went beyond the prepared talking points to explain the administration's version of the "misunderstanding." He said it arose in part because Reagan wanted to avoid addressing the question of what the United States would do if missile defense technology was proferred to the Soviets and then refused by them.

Asked what the United States would do, Speakes replied, "Who knows? That's at least two presidents down the road."

Even enthusiasts of the missile defense program acknowledge that its probable accomplishments often have been overstated by the president. For example, Reagan describes the system as one that would provide a shield for civilians against nuclear missiles without acknowledging that, by itself, it is unlikely to protect against low-flying cruise missiles and bombers.

Most recently, Reagan has been saying that the system would need to remain in place after nuclear missiles are eliminated as protection against a "madman" someday launching a nuclear missile. But the shield does not include a defense against ground-based terrorists.

At a recent campaign rally in Milwaukee, Wis., Reagan used an anecdote to explain his vision of strategic defense.

He said U.N. Ambassador Vernon A. Walters was on a mission to China, where officials spoke critically to him of the concept of a "strategic shield."

"He said, if a man has invented a spear that can penetrate any shield, and another man has invented an impenetrable shield and they meet, what happens?" Reagan said. "And Ambassador Walters said, 'I don't know the answer to that. But I do know what happens if a man with a spear that can penetrate anything meets a man who doesn't have a shield at all . . . . "

Reagan said the Chinese then "sort of changed their mind about our defense program."