Martin Marietta Corp. said yesterday it will start buying Bendix Corp. stock next week even if Bendix already has purchased Martin Marietta shares under its rival offer.

The Bethesda-based aerospace conglomerate also said it has been offered more than $500 million in additional credit for the takeover battle from a group of financial institutions. The company already has a $930 million credit arrangement in place and credit lines for another $200 million.

Bendix, meanwhile, released details of a suit filed Friday in U.S. District Court in Baltimore seeking to stop United Technologies Corp., which has joined Martin Marietta in the fight against Bendix. The suit charges that a UTC takeover of Bendix would cause antitrust problems in a dozen business areas, including fuel controls for gas-turbine engines, jet engine starters and aircraft flight-control systems.

UTC said in response that it had anticipated those problems, and that was why it had agreed to sell parts of Bendix to Martin Marietta.

Bendix started the three-way battle three weeks ago by offering $48 a share for Martin Marietta. Martin Marietta countered with a $75-a-share offer for Bendix, and United Technologies last week made its own $75-a-share offer for Bendix -- contingent on a collapse of Martin Marietta's and Bendix's offers. Bendix can begin buying the company's stock Friday. Martin Marietta can begin buying Bendix stock Sept. 23.