U.S. and Soviet arms control negotiators resumed their talks here today amid indications that the continuing deadlock over President Reagan's Strategic Defense Initiative will block significant progress.

The two sides met for an hour and 50 minutes at the Soviet Mission here. As usual, no statement was issued after the talks and the U.S. delegation even abandoned its traditional practice of announcing the date of the next meeting. A spokesman said simply that this was "a change of plan."

Informed sources said the next meeting appeared to be scheduled for Friday at the U.S. delegation's offices, but this could not be confirmed. A Soviet spokesman, asked when the next meeting would be, said, "Ask the Americans."

Chief Soviet delegate Viktor Karpov and American negotiator Max Kampelman traded small talk during a photo session before getting down to business.

In an airport arrival statement yesterday, Karpov had indicated that the Soviets are not interested in cutting nuclear weapon levels unless Washington abandons research on the Reagan space defense plan, popularly known as "Star Wars." Progress in the current round of talks depends on "the necessary adjustments in the U.S. position," he said.

Today, talking informally with reporters before the first session, Karpov said that "stopping the arms race in space was a goal set by Soviet Foreign Minister Andrei Gromyko and Secretary of State George P. Shultz" when they met in Geneva in January. "So we feel that both our countries should now practically agree on how to do so," he said.

Kampelman confined himself to saying that "we hope this session will be a constructive one." In an arrival statement the previous day, however, he had said that his instructions from President Reagan "are not basically in any way altered." Reagan has said that research on "Star Wars" will continue even though the United States is prepared to discuss it in Geneva.

Soviet leader Mikhail Gorbachev's offer yesterday to make cuts in the Soviet Union's nuclear arsenal if the United States will abandon the "Star Wars" project appeared to have underlined Moscow's intention to stay firm in the talks here, according to western observers. The offer was made in the context of talks in Moscow between Gorbachev and visiting Italian Prime Minister Bettino Craxi.

Six members of a U.S. Senate delegation attending the meeting as observers -- they are not allowed to attend the formal negotiating sessions -- said they were "here to demonstrate once again the commitment of the United States Senate to the arms control process."

Sen. Ted Stevens (R-Alaska), spokesman for the group, said, "Our negotiators have the flexibility to negotiate seriously and comprehensively with the object of achieving equitable and verifiable agreements which meet the security interests of both nations."