MOSCOW, OCT. 14 -- A major economic parley between the Soviet Union and its key allies ended here today with a decision to end gradually the mandatory use of the Soviet ruble as the sole currency of trade among them.

The East Bloc trade alliance, called Comecon, adopted a program to buttress trade among the 10 member countries, starting with changing some of the rules and streamlining some of the bodies that regulate their exchange of goods, a spokesman for the organization said.

"Certain branches" of the organization will be abolished, said Vyacheslav Sychev, a Comecon official, while other branches will be expanded. He did not give details.

The Comecon leaders also agreed to improve cooperation within the bloc and pave the way for more trade with Western Europe. Comecon includes all of the countries in the East Bloc, plus Cuba, Vietnam and Mongolia.

The meeting, attended by prime ministers of the member countries, agreed to replace the ruble with another monetary unit as the currency used to set the value of goods bought and sold among Comecon members. "However, this will require a certain time," Soviet Premier Nikolai Ryzhkov told the Comecon delegates.

In the meantime, the countries agreed to allow more widespread use of their own currencies, in addition to the ruble, for conducting trade. With the ruble as its currency, Comecon's trade policies have favored the Soviet Union.

Closer trade ties between Comecon and the European Community are well under way, a Comecon spokesman said. Ways to further integrate the smaller countries -- Mongolia, Cuba and Vietnam -- into Comecon also were discussed, officials said.

In addition to the smaller countries and the Soviet Union, Comecon's members are Poland, Hungary, Czechoslovakia, East Germany, Bulgaria and Romania.