By a 1-vote margin, 43 to 42, the Senate yesterday, after and extraordinary closed-door session, defeated an effort by Sen. Mark O. Hatfield (R-Ore) to prohibit funds in the fiscal 1978 public works money bill from being used to produce a new generation of neutron enhanced radiation weapons.

By the same vote, it approved Language proposed by Sen. John C. Stennis (D-Miss) to freexe those funds until President Carter decides if he wants to go ahead with production and Congress is sent an arms-control impact statement on the new weapons outlining what effects with the Soviet Union.

Left pending until after the July Fourth recess were other amendments that would give Congree the right to veto a Carter production decision.

For almost six hours yesterday, the Senate debated whether to procede with the firs generation of tactical nuclear weapons specifically designed to kill people primarily through radiation rather than destroy enemy installations and equipment through blast and heat.

A neutron warhead, by emphasizing radiation rather than blast, produces much less collateral damage off the battlefield than nuclear weapons now in the Army inventory.

Stennis said yesterday that the new enhanced-radiation warhead "has the radius of a pistol shot rather than the radius of a shotgun . . . The idea of having this weapon is the best news I've had in years," he said.

"It will relieve the probable human kill and at the same time carry a tremendous deterrnet force," he said.

Hatfield said the new neutron weapons "introduce a whole new dimension into nuclear warfare."

The fact that they limit cooateral damage. Hatfield added, "invites their use. He argued that once the United States employed such a weapon, the soviets would not be inhibited from using theirs.

"My ultimate hope," Hatfield said, "is that this weapon never senters the arsenal."

Sen. Henry M. Jackson (D-Wash) another supporter of the new weapons, said during debate that they "would enable the U.S. and its NATO allies to confine the lethal effects to the immediate military objectives, sparing the innocent and protecting our own soldiers."

Two and one half hours were spent in closed session, the first the Senate has had since 1975. Stennis, chairman of the Senate Armed Services COmmittee and floor manager of the public workds money bill, moved to close the Senate session so classified details on the enhanced-radiation weapons and their cost could be laid out to the members.

Although no figures discussed during the closed session leaked out, it was learned from other sources that the Army's proposed total costs for developing and producing neutron 8-inch artillery projectiles is $650 million.

Costs associated with the neutron warhead for the Lance missile system the other weapon set for production - were not available.

During the debate, it was disclosed that the President had moved up to Aug. 15 the target date for his decision on neutron weapon production. It had been orginally set at Oct. 1.

Hatfield said that the arms control impact statement on the Lance warhead which had been requested for yesterday's Senate debate would not be produced by the administration until after the President decides whether he will go ahead with production.

Failure of the Ford administration to send COngress the arms impact ataement on the Lance neutron warhead - as required by law - wa an oversight, according to Stennis. "It was prepared but misplaced," he siad.

Hatfield drew some of his support, however, from senators who were not against the enhanced-radiation weapons but rather were disturbed by the system through which it had been approved.

Hatfield said he had first learned of the new weapons through news stories and that when he asked questions of Senate Staffers and members, he found "none not be passed in a cursory fashion."

"This he lost in the initial test by a single vote. Hatfield moved a new amendment that would allow either the Senate or the House 60 days to veto a Carter decision to go ahead with production.

Sen. Sm Bunn (D-Ga), a strong prponent of the new enhanced-raditaion weapons sought to amend that proposal by requiring bothe the House and the Senate to vote against the President's production decision in order to veto it.

Yesterday's session ended with agreement to continue the debate after the Senate comes back into session July 11.

Though Hatfield lost his bid to block production now, he said after the session yesterday that he was satisfied the matter had been brought to the attention of the Senate and the public.

Although the House has already approved the public works money bill with the neutron weapon production money intact, it has not passed the Energy Research and Development Administration's military applications authorization, which also contains reference to the new weapons.

A move is expected to be made in the House, smiliar to yesterday's in the Senate, to give the members some vote on the neutron weapons.