President Carter's decision, released yesterday, to defer immediate production of neutron weapons and await a Soviet response seemed to cool down many but not all congressional critics who feared the program was going to be cancelled.

To give proof that a real neutron option continued to exist, administration officials pointed out that the president's program requirs establishment of production lines for building new 8-inch artillery shells and Lance missile warheads - lines that within the next year could be fixed to turn out either nuclear or neutron versions of those weapons.

While reactions on Capitol Hill could be measured somewhat, it was more difficult to assess the long-term political fallout that may come from the apparent presidential vacillation that preceeded the long-delayed neutron decision.

Senate Majority Leader Robert C. Byrd (D-W. Va.) yesterday seemed to illustrate one type of congressional reaction.

On Thursday he wrote Carter warning that scrapping the nuetron option without a Soviet tradeoff was "naive" and would jeopardize a Strategic Arms Limitation Talks (SALT) agreement ratification in the Senate.

Yesterday, after being informed of Carter's decision, Byrd said he would have rather gone ahead with production but that Carter "is on solid ground . . . if he can secure concessions from the Soviet Union that are verifiable."

Administration sources yesterday stressed that they will actively search for some arms control arrangement that would avoid having to go to the neutron option in future months.

"We will welcome initiatives by the Soviets in this regard," one administration officials said yesterday, adding, "This is a time of testing their intentions."

This source said there were no specific proposals in mind to make to the Soviets, but that some might be forth-coming after discussions with the NATO allies. He specifically ruled out linking it with the current SALT negotiations.

He suggested, however, that continued Soviet or Warsaw Pact military buildup along the NATO front might trigger a decision to go the neutron option.

In his statement, Carter said his "ultimate" decision on neutron production "will be influenced by the degree to which the Soviet Union shows restraint in its conventional and nuclear arms programs and forcr deployments affecting the security of the United States and western Europe."

Sen. Sam Nunn (D-Ga.), who with Carter's support last year led the Senate fight to secure funding for neutron weapons, was sharply critical of the president's decision.

"At this point we don't have a bargaining chip," Nunn said. "We have an invisible chip with Soviets."

"Why would they negotiate away a weapon they are willing to produce for one we don't have to courage to producr?"

Nunn also hit at another point: why Carter had not gone ahead with his earlier position, one of immediate production with negotiations with the Soviets before deployment.

"Europeans had reached a point," Nunn said, "where they were willing to support a production decision . . . with a commitment that we would deploy the weapon if we did not get any agreement with the Soviets."

Administration sources took issue with Nunn's analysis and yesterday spent a good deal of time trying to reconstruct the various positions of the president and the allies that led up to yesterday's final decision.

The president, since last June, when existence of production plans for neutron weapons became public, initially was prepared to order them built.

A decision at that time to consult with the NATO allies was expected to be perfunctory.

Those negotiations began to drag on when NATO leaders, particularly in West Germany, measured the public reaction again weapons being stationed on their soil which were to be used there and not in Warsaw Pact countries.

Opposition grew also because of a propaganda campaign promoted by the Soviets.

In mid-March, these administration sources said, Carter ordered a review of the neutron production situation.

Some sources said this was the first time the president had taken a close look at the negative as well as the positive side of the neutron question.

A key issues raised by that revies,sources said yesterday, was "expressions of reticense" on the part of some NATO countries toward deployment of neutron weapons on their soil.

Some sources singled out the Germans and others said no, it wasn't just the Germans.

One administration source said the Germans had agreed to production said the Germans had a agreed to production and deployment but before they went along finally required another "continental" power to agree - a definition that would rule out England, which apparently was ready to go along with a deployment decision.

In any case, the source said, Carter by last week was not about to go ahead with immediate production even if NATO deployment were assured.