Dow Chemical Co. and Martin Marietta Corp. are planning a joint venture to produce specialty chemical products in the steel, chemical and snow-and-ice-removal industries, the companies said yesterday.

The joint venture, which the companies expect to generate annual sales exceeding $200 million, will enable Marietta and Dow to compete more effectively with magnesia imports, company executives and analysts said.

"This consolidation of companies in a relatively stagnant industry is an attempt to improve their cost position so they can compete more effectively against magnesia imports from countries such as Jordan and Israel," said James H. Wilbur of Smith Barney, Harris Upham & Co.

Under the proposed venture, the two companies will jointly produce refractory chemicals, which are used mainly in the steel-making industry to line and protect the walls of furnaces; ice-removal materials; oil additives and dust supressors.

Dow, which is based in Midland, Mich., will contribute its magnesium hydroxide and calcium-chloride production facilities at Ludington, Mich., to the venture. Marietta, which is based in Bethesda, will contribute its Manistee, Mich., production facilities for magnesia chemicals and specialty products and its limestone plant at Woodville, Ohio, plus other assets at River Rouge, Mich., and at Bridgeport, Conn.

The venture is not expected to have a significant impact on Marietta, whose business is concentrated in the aerospace industry, according to analysts.

"Frankly, I don't think this will mean very much for Marietta," said Edmund S. Greenslet of Merrill Lynch, Pierce, Fenner & Smith. "Activities out of the aerospace industry are a very small part of the company's business."

Marietta's magnesia-specialty business has "kind of hung in there with less than $5 million in profit over the last couple of years," said Robert D. Kugel of Morgan Stanley & Co. Inc. "It is one of the smallest units of the company, and has not been particularly profitable because of depressed conditions in the steel industry."

Magnesia chemicals and other products not associated with the aerospace industry represented about 7.5 percent of Marietta's business -- or sales of about $333 million out of total company sales of $4.4 billion last year, Greenslet said.