The Carter administration abruptly changed course last week and called off negotiations in Brussels with its European NATO allies specifically designed to court their public support of U.S. production of neutron artillery shells and missile warheads.

Allied governments, on whose soil the neutron weapons would be deployed, have been skittish about giving open backing to the controversial new generation of tactical nuclear weapons because of political opposition to them that has developed within their coutries.

President Carter has made it clear up to now that he would not order production unless he could count public NATO government support of his decision.

Although some administration sources maintained yesterday that the President has not yet made his final go-ahead decision, the talks which had been under way for several weeks were based on a preliminary White House determination that a production order would be made by mid-April.

"That decision had been made some time ago," one source said yesterday, "but now we are in a holding pattern."

A few government officials interpreted the talks cancellation last week as a sign the president has reversed himself and is now leaning against a neutron go-ahead. Others, however, said Carter has only made "a decision to delay the decision," in the words of one.

Nuclear shells and warheads now deployed in Europe destroy targets such as tanks and fortifications primarily through heat and blast.

Proposed neutron 8-inch artillery shells and Lance missile warheads, on the other hand, cut down blast and heat and are designed to kill or incapacitate enemy troops primarily by radiation.

Proponents of the weapons say they would be more credible deterrents in Europe than those now deployed because they would cause less collateral damage to towns and cities adjacent to battlefields.

Opponents argue the new weapons would lower the nuclear threshold since battlefield commanders would ask to be able to employ them earlier than they would the more destructive nuclear artillery and missiles.

There was some consternation at the State Department because of the sudden White House decision last week to pull back from the neutron productions discussions.

A great deal of diplomatic effort had gone into moving West German Chancellor Helmut Schmidt and British Prime Minister James Callaghan closer to speaking out in support of production.

According to one source, a high-level Carter aide will go to Europe soon to explain the president's new course.

To date, no Western European country has approved the neutron weapons. The Netherlands, the only country whose parliament voted on the issue, recently turned them down.

The Soviet Union, meanwhile, has tried to make the proposed building of neutron weapons by the United States an international issue. This campaign, picked up by communist parties in Western European countries, has added to the problems of NATO political leaders.

Because of the international political controversy that has developed around neutron weapons and the president's seven-month delay in making his promised production decision, White House and other government officials are extremely sensitive about discussing the matter. Yesterday, for example, officials repeatedly requested during interviews that they not be quoted by name or even agency.

There was no consensus on how long the current "holding pattern" would last.

"It might be two weeks, a month or longer," one official close to the decision-making process said.

Another suggested meetings within the government will take up "other options. We may go ahead with production without the allies' support."

Up to now that course has been avoided for several reasons.

One is that Congress by law has 45 days to vote by joint resolution to overturn a decision to build the weapons.

Opponents on Capitol Hill could make use of allied failure to support the president as a sign that Congress should turn against the weapons.

Carter also is said to want NATO support because of the upcoming United Nations debate on disarmament, where the Soviets are bound to criticize a move to neutron shells. The president reportedly does not want to stand alone among world leaders in favor of building neutron weapons.