Senior Soviet officials disclosed yesterday that production of SS-24 strategic missiles for deployment on rail cars will end by Jan. 1, a move that appears to abbreviate the life of a Soviet military program the United States had tried to eliminate through negotiations.

The planned termination of SS-24 missile production was announced by Soviet Foreign Minister Eduard Shevardnadze as he concluded two days of talks with Secretary of State James A. Baker III in the Siberian city of Irkutsk. Baker said he welcomed the Soviet move but that it would not lead to any shift in the current U.S. position at superpower arms-control talks.

U.S. officials said the Soviet announcement was foreshadowed in a secret May proposal to President Bush by Soviet President Mikhail Gorbachev, in which Moscow promised to cease SS-24 production if the United States gave up its plan to deploy a similar, mobile missile on land. That proposal was rejected by Washington as one-sided.

Shevardnadze said production of the SS-24s for deployment aboard rail cars "was basically completed," but he did not specify any numbers. However, another senior Soviet official said in an interview that the program would likely end after 36 missiles had been deployed aboard special military trains operating periodically on Soviet commercial railroad lines.

The Soviet official, who spoke on condition that he not be identified, indicated that each train carries three missiles and that a total of 12 trains would be situated at three different points in the Soviet Union. He said also that the 360 nuclear warheads atop these missiles would represent less than 3 percent of the current Soviet strategic arsenal and less than 6 percent of the Soviet warheads remaining after implementation of a new U.S.-Soviet arms treaty later this decade.

U.S. military officials said earlier this year that at least nine such trains had become operational since 1987 and predicted that the Soviets would deploy at least 18 trains carrying SS-24 missiles. No mobile, land-based strategic missiles are deployed by the United States.

In May, the Bush administration asked the Soviet Union to scrap its entire force of rail-based SS-24 missiles to limit the possibility of their illicit production and deployment. Mobile missiles such as the 10-warhead SS-24 are considered more difficult to monitor than those deployed in underground silos, and they are also far more difficult to target in a nuclear attack.

President Bush, acting on the recommendation of his national security adviser and under pressure from key members of Congress, had promised in return not to move 50 U.S. MX missiles from underground silos to rail cars under a plan that was to begin next year. But the House and Senate armed services committees voted recently to kill the MX rail plan, on grounds that it costs too much and is no longer needed to reduce the risk of nuclear war.

Baker noted that the Soviet decision maintains the existing U.S.-Soviet disparity in mobile-missile deployments. However, Vitaly Churkin, a senior adviser to Shevardnadze, told reporters in Moscow that the Soviet move was significant because it will simplify monitoring of the expected new U.S.-Soviet strategic arms treaty.

One U.S. official said the move could be interpreted favorably as a sign that Moscow does not place great emphasis on its mobile force of SS-24 missiles and may be willing to scrap them under a subsequent arms accord. He added that the move might also be interpreted unfavorably as a sign that Moscow is determined to maintain a modest advantage in such weaponry in the wake of a lack of congressional interest in a matching U.S. program.

Washington Post staff writer Al Kamen in Irkutsk and correspondent Gary Lee in Moscow contributed to this report.