The Belgian government, moving to defuse a revolt within Prime Minister Wilfried Marten's political party, announced a postponement today of its decision on whether to deploy cruise nuclear missiles until after Martens visits Washington in mid-January.

A government communique issued after a Cabinet meeting said the decision would be made during the first three months of 1985. A spokesman for Martens said the Belgian leader wanted first to get a report from President Reagan on the talks between Secretary of State George P. Shultz and Soviet Foreign Minister Andrei Gromyko scheduled for early January.

Belgium has always said it would deploy the cruise missiles, in accordance with NATO's 1979 plan to install new medium-range nuclear weapons in five West European countries, but has delayed a final decision while waiting to see if U.S.-Soviet talks to limit the weapons would succeed.

Earlier this month, the government set March 1985 as the date to begin deployment, barring a last-minute revival of the talks in Geneva that the Soviets left last year. But following the announcement last week that Shultz and Gromyko would confer, Martens' own Christian People's Party called on the government to give the U.S.-Soviet talks "a chance."