In an atmosphere of unusual amity, the Senate yesterday approval a $35.9 billion authorization for defense procurement in fiscal 1978 by a bote of 90 to 3.

In contrast to past savage fights over slashing the defense budget, not a single amendment to cut the weapons bill was offered.

The amount in the bill is virtually identical to President Carter's request and the figure in the House bill, though some details differ.

Sen. John C. Culver (D-Iowa), long a Pentagon critic but a supporter of the bill, said the absence of major attempts to cut it resulted from the fact that Carter had asked $2.8 billion less than his Republican predecessor, had deferred a full-speed go-ahead on the B-1 bomber and various other big weapons systems and had placed more emphasis on combat readiness - thus doing in advance what many Pentagon critics wanted.

Others said there also is more concern in Congress over reports of a Soviet arms buildup and that Carter is getting the benefit of the doubt from some Democrats, who might have sought to slash figures proposed by a Republican president.

Both the House and the Senate bills include more than $1 billion to start producing five B-1 bombers, but action on whether to go ahead with the proposed 244-plane fleet awaits a June recommendation by Carter.

A major difference between the bills is Senate inclusion of $81.6 million for advance procurement on a possible forth Nimitz-class nuclear carrier, with the understanding that parts could be used for other ships if it is decided not to build the carrier. Neither Carter not the House provided for this money.

The Senate provided $95 million for civil defense, the House $135 million. Carter had asked $80 million.

Sen. William Proxmire (D-Wis.) proposed to enlarge the noncombat and semicombat jobs available to women in the armed forces, including letting them serve as Air Force missile launch officers who could press the nuclear button. Proxmire settled instead for a six-month Defense Department study.