West German Chancellor Helmut Schmidt's Social Democratic Party strongly criticized President Reagan's decision to proceed with manufacture of neutron weapons yesterday, calling it an obstacle to East-West arms control and a source of "new arguments" for anti-Americanism in Europe.

The party position, against a background of cool reserve in other European capitals, reflected public unease in several NATO countries over the new generation of nuclear weaponry and a belief among European officials that sooner or later the United States will renew its request that the controversial warheads be stationed on European soil.

"The federal West German government is requested to insist during the necessary alliance negotiations that a position be taken that this weapon not be brought to deployment in Europe," the party said in a statement relayed by news agencies.

Although the party position is separate from that of the government, the statement was signed by Hans-Juergen Wischnewski, the party's deputy chairman and a confidant of Schmidt. Schmidt's government in Bonn, in its only public reaction so far, noted that while the decision to manufacture neutron arms is a domestic U.S. matter, any attempt to deploy it in Europe would have to be negotiated between Washington and its NATO allies.

In more lining up for what is expected to become a difficult debate for Schmidt, his conservative opposition, the Christian Democrats, defended Reagan's decision as "a necessary answer to excessive Soviet arming." The Free Democrats, partners in Schmidt's coalition, said the U.S. move underlines the need for comprehensive arms controls.

This is a politically charged issue for other European governments as well because of the weapon's characteristics -- it aims at people rather than leveling vast areas -- and because its main mission in Europe would be to repel a Soviet advance on European territory. In addition, a widespread movement is questioning the wisdom of deploying more nuclear weapons of any kind in Western Europe.

In the Netherlands, where this antinuclear feeling is particularly strong, about 30 young protesters marched outside the U.S. Embassy in The Hague with signs saying: "Stop the Neutron Bomb. Stop the Nuclear Arms Race." A brief demonstraton also was reported outside the U.S. Embassy in London.

Official statements in Britain and the Netherlands, as well as in West Germany and Italy, emphasized that as long as the U.S. decision concerns only production of neutron weapons and stockpiling in the United States, it is a U.S. decision and does not require consultation with allies.

The Dutch government complained about short notice from Washington, however, and Denmark and Norway openly criticized the decision -- the only NATO governments to do so. Their Scandinavian neighbor, non-NATO Sweden, labeled the decision "a dangerous escalation" of the arms race, Reuter reported from Stockholm.

In France -- a North Atlantic Alliance member although not a participant in the North Atlantic Treaty Organization's integrated command -- Defense Minister Charles Hernu reminded his countrymen that the Soviet Union and France also have experimented with neutron weapons. He called the Reagan decision "ambiguous" because it talks only of manufacture and stockpiling without approaching directly the politically explosive subject of deployment.

"It is a tactical weapon of theater operations and even, possibly, of the European theater, and this is the crux of the problem," he added, according to news agencies. "France, not being a NATO member, is not directly concerned by President Reagan's decision, but France is in Europe and cannot remain indifferent."

Some officials cited in reports from European capitals voiced particular criticism of the decision's timing, declaring that it could complicate efforts to begin negotiations with the Soviet Union over the medium-range nuclear weapons. Others, however, said the timing could also give the Reagan administration another card to play in the talks on medium-range nuclear arms.

Reagan, after urging from European allies, pledged recently to begin medium-range missile talks with Moscow by the end of the year. The Associated Press reported from Moscow that a Soviet Foreign Ministry official indicated these talks could be affected by the neutron decision.

"I cannot be certain what the effect will be since the talks have not been held yet," the unidentified spokesman said in response to a query. "But the possibile effect can be judged by our negative reaction to the decision to produce neutron weapons."

The official Soviet news agency, Tass, renewed Moscow's criticism of Sunday, calling the decision the latest step "in the campaign of silence, lies and deception which has long been used by the United States to cover up development work on this most inhuman variety of mass-destruction weapons."

In a dispatch from Washington, Tass said the decision shows that the United States had been planning all along to produce the arms. When he was president, Jimmy Carter originally planned to manufacture them and station them in West Germany. In 1978 he reversed himself and put off the decision, partially in response to strong public objections in Western Europe.