The U.N. General Assembly wound up a five-week special session on disarmament yesterday by approving a proposal to enlarge the Geneva disarmament conference and create a rotating chairmanship.

The United States and the Soviet Union agreed to give up their joint chairmanship of the conference as part of an effort to get France and China to take part in the Geneva disarmament talks.

The 31-nation conference - which was organized by the United States, Britain, France and the Soviet Union in 1959 - has been the forum for the drafting of treaties on germ warfare, nuclear nonproliferation and installation of nuclear weapons on the ocean floor.

France withdrew from the conference during the de Gaulle era, complaining that it was dominated by the two superpowers. A number of other participants have frequently charged that the United States and the Soviet Union conduct most of the real bargaining in bilateral negotiations.

When the new disarmament conference - which will have 37 to 40 members - meets next January, the chairmanship will rotate each month among all participants in alphabetical order.

In Paris, a French Foreign Ministry spokesman welcomed the decision and indicated that France would now be prepared to end its boycott of the conference.

There was no immediate indication that China would also decide to take part in the reorganized conference.

The decision to create a more representative disarmament conference was seen as one of the main achievements of the special session of the General Assembly, which was due to adjourn late last night.

The General Assembly's working committee of the whole approved a final 28-page document without a vote early yesterday, assuring its adoption.

Several controversial proposals were shelved by the working committee to preserve a facade of unanimity.

One proposal, sponsored by Iraq and 31 other nations, called for a mandatory arms embargo against Israel. The sponsors agreed not to demand that this proposal be put to a vote on the understanding that the resolution would be considered when the General Assembly holds its regular session in the fall.

India also agreed not to press resolutions calling for a moratorium on the testing of nuclear weapons and a ban on their use.