A company headed by Dallas businessman Harold Simmons offered yesterday to buy Sea-Land Corp. for $25 a share cash, or a total of $580.8 million.

Contran Corp., a Dallas-based diversified holding company headed by Simmons, said that the offer is subject to various conditions, including completion of financing and acceptance of the offer by Sea-Land.

Sea-Land, based in Menlo Park, N.J., is an international transportation services company and one of the largest U.S. flag carriers of containerized shipping. The company said that its directors will consider the offer at a regularly scheduled board meeting Monday.

Sea-Land's stock, the second most active in New York Stock Exchange trading yesterday, closed up 2 1/2, at 24 3/8.

Simmons has been buying Sea-Land stock on the open market since last July when he disclosed plans to acquire 15 percent of the company's 23.23 million shares outstanding. As of yesterday, his Amalgamated Sugar Co. of Odgen, Utah, held about 10 percent of Sea-Land's stock, according to J. Landis Martin, Simmons' attorney.

In July, Joseph F. Abely Jr., Sea-Land's chairman and chief executive, had called Simmons' interest in the company "most unwelcomed." He would not comment yesterday on the new offer.