Copper industry workers looking for wage increases similar to those negotiated earlier this year with steel and aluminum companies will strike Friday unless copper companies substantially increase the existing contract offers, a spokeman for a coalition of about two dozen unions said today.

"The clock is ticking and we're working against the strike deadline and there is no offer on the tables of the copper company that the union finds acceptable," said Cass Alvin. Alvin is the spokesman for the United Steelworks of America, which represents the largest number of workers in the coalition.

Three-year contracts expire at midnight Thursday between unions and the Anaconda Co., Asarco, Inc., the Cities Service Co., Inspiration Consolidated Copper Co., Kennecott Copper Corp. and the Phelps Dodge Corp. Contracts with the Magma Copper Co. expire a day later, and others terminate July 31 with Anamax Mining Co., Aug. 31 with Cyprus Pima Mining Co. and Sept. 30 with the Duval Corp.

Union representatives are asking for straight-time pay increases totaling about 94 cents an hour over the next three years. Their demands are similar to contracts accepted April 9 by steel companies and May 24 by major aluminum producers.

Company offers have been much smaller, with Phelps Dodge, the largest copper employer in Arizona, offering an increase of slightly more than 25 cents an hour in straight-time wages, according to M.P. Scanlon, the company spokesman. The average industry wage in April was $7.52 an hour.

A walkout would have the largest impact in Arizona, which produces most of the country's copper, but it also would affect activities in Utah, New Mexico, Nevada, Montana, Washington, Idaho, New Jersey, Texas and Maryland, Alvin said.

He estimated that 20,000 copper workers in Arizona and about 40,000 workers nationwide would be affected by a strike, although workers in some right-to-work states are not union members.

Copper workers have walked out each of the last three times their contracts expired. The longest strike began in mid-1967 and lasted more than eight months.

A strike this year is "very likely - almost a certainty," Leaming said. "The conditions are just right for it on both sides."

The non-ferrous industry conference, a policy-setting group that includes representatives of all unions affected by the contract negotiations, will begin meeting Thursday afternoon in Phoenix.

If no settlement is reached by contract deadline, the conference will either recommend an extension - which Alvin says is "not very likely" - or a strike.