The U.S. operations being included in the proposed sale of 12 business units of Alcan Aluminium Ltd.'s U.K. subsidiary, British Alcan Aluminium Plc, involve seven plants in New Jersey, Pennsylvania and California employing about 550 workers.

The East Coast units include Reade Manufacturing of Lakehurst, N.J., which makes and markets magnesium particulates, and Alcan units in Flemington, N.J., and Aspers, Pa., specializing in the production and sale of zirconium chemical products for flame-proofing, antiperspirant, paper coating and other applications.

Also on the block are Luxfer USA, which produces high-pressure compressed gas cylinders at plants in Riverside and Placentia, Calif., and Graham, N.C.; and the Superform USA facility in Riverside which makes superplastic aluminum pressings for aerospace and architectural applications.

Montreal-based Alcan Aluminium said last week that it had entered exclusive negotiations to sell the 12 business units, which have 35 locations in the United Kingdom and one in Ireland, as a single group.

The intended buyer was identified as a new company formed by Mercury Asset Management Plc's development capital arm, Mercury Development Capital. There has been speculation that the package eventually would be broken up, although Lazard Brothers, which since last March has been helping British Aluminium sell the package, reportedly indicated last week that this was far from decided and a Mercury spokesman dismissed the idea of any immediate unbundling.

Other operations involved in the 12-business package include the production and marketing of aluminum extrusions, wire and cable, plate and household foil.