MONTREAL, SEPT. 15 -- Diplomats from 45 nations late today swept away the final obstacles to an international agreement designed to halve within a decade the industrialized world's consumption of ozone-depleting chemicals.

The U.N.-sponsored conference convening here is expected Wednesday to approve the agreement, which would curb chlorofluorocarbons (CFCs), the chemicals that break down the ozone layer of the stratosphere. That upper atmosphere ozone serves as a barrier to cancer-causing ultraviolet radiation.

The agreement would represent the first international air-pollution controls.

"There is a high likelihood of a protocol tomorrow {Wednesday}," said Winfried Lang of Austria, the conference chairman. He said last-minute obstacles were resolved in intense negotiating sessions.

Lang said that under compromises worked out in the negotiations, the Soviet Union would be given "special treatment" that permits increases in production and consumption of CFCs in line with its ongoing five-year plan and the nations of the European Economic Community would be treated as a unit for purposes of the agreement.

Today's negotiating breakthrough caps a nine-month effort to restrict CFCs -- gaseous chemicals used in a vast array of products, ranging from air conditioners to solvents that clean computer chips. About $750 million in CFCs are produced annually in the United States.

Unlike other pollutants, the CFCs do not break down in the lower atmosphere. In the upper atmosphere, they release chlorine that erodes the stratospheric layer of ozone, which protects against the harmful effects of ultraviolet radiation, including skin cancer, eye disease and crop damage.

The agreement, which would become effective a year after its ratification by nations representing two-thirds of the world's CFC consumption, would freeze each participating nation's consumption at 1986 levels. Four years later, the parties would be required to reduce their consumption by 20 percent and six years later by another 30 percent.

An exception would be granted to less-developed nations whose annual per capita consumption of CFCs is below two-thirds of a pound. They would be permitted to import enough of the chemicals to bring their consumption up to that level.

To accommodate increased consumption in the Third World, producer nations would be able to increase CFC output by 10 percent over 1986 levels. But they would be required to cut production when consumption cuts become effect four and six years after ratification.

Except for exports to the Third World, the agreement would provide a number of controversial trade restrictions, including a ban on imports of bulk CFCs from nonsignatory nations within a year of ratification and a ban four years later on imports of products containing the chemicals.

The trade restrictions were the most contentious issue resolved today, involving the largest CFC producers -- the United States and the EEC nations, which manufacture 30 percent and 45 percent of the world's output of the chemicals, respectively.

The EEC insisted on being treated as a unit, permitting some members to exceed the limits as long as the community as a whole complies.

Representatives of the 12 member nations of the EEC argued that such an exemption is necessary to uphold the provisions of the community's 30-year-old charter. Under the proposed CFC pact, nations that reach their consumption ceiling would be prohibited from importing more of the chemicals.

U.S. officials objected to treating the European Community as a whole, claiming that such action could give an unfair advantage to certain European producers in competition with U.S. manufacturers.

The Soviet Union, which represents about 10 percent of world CFC output but consumes much less, threatened to boycott the agreement because its limitations interfered with its five-year plan to construct new CFC plants by 1990.

Lang said the problem was resolved by permitting increased production of the chemicals from Soviet plants under construction before last January. But the new output cannot raise annual per capita consumption of CFCs in the Soviet Union higher than 1.1 pound.