Chancellor Helmut Schmidt, in his first public comments on President Reagan's decision to produce neutron weapons, bucked the opposition of his own Social Democratic Party yesterday and reaffirmed his support for the stationing of such weapons in Western Europe.

The West German chancellor said he stands by the decision he made in 1978 to allow the United States to deploy the weapon if three conditions were met.

These were that West Germany should not be the only country to accept such weapons, the the decision be made by the North Atlantic Treaty Organization as a whole and then only if arms control negotiations with Moscow failed to achieve results.

"In principle I do not see that the federal government should make any basic change in its opinion," Schmidt said.

Meanwhile, in Moscow, a senior Soviet commentator raised the possibility that the Soviets may consider building a neutron warhead in response to the U.S. decision.

Yuri Zhukov, an alternate member of the Communist Party Central Committee, stressed in an article in the party daily Pravada, a warning issued by President Leonid Brezhnev in April 1978 that the Soviet Union would not "begin production of neutron arms so long as the United States does not do so."