Martin Marietta Corp. President Thomas G. Pownall said yesterday that the Bethesda aerospace company is discussing with several possible buyers the sale of its cement division for about $300 million.

Pownall said in an interview that Marietta is pursuing the sale to help raise cash to reduce the $900 million debt it acquired fighting a takeover attempt by Bendix Corp. last summer. But he said nothing is definite regarding the cement operations, and he would not estimate when a transaction might be completed.

"We're talking about something in the $300 million category, so it's not something that's done in the snap of a finger," he said.

Sources have said the corporation has been negotiating with Swiss and German companies for sale of the cement operation, and Pownall said foreign and domestic companies had been bidding.

He also said that Marietta is talking with other companies about some of its nonaerospace divisions, "which may result at some time in the future--the future meaning in the next couple of months--in an opportunity to sell some other assets." He gave no other details, but said that Marietta is not trying to unload less-profitable properties just to raise money.

"We would like to have an opportunity to bring our debt down. But we are not looking for an opportunity to sell our assets at a loss."

The month-long battle with Bendix--one of the bloodiest and most celebrated takeover battles in history--left Martin Marietta with a tattered balance sheet and a new part-owner: Allied Corp.

In the agreement that ended the complicated merger fight, Allied took over Bendix and swapped Bendix's 70 percent stake in Marietta for Marietta's 51 percent holding in Bendix. Allied now holds 39 percent of Marietta's stock and will nominate two members of the company's 15-member board.

Pownall said he has had no contact with former Bendix chairman--now Allied president--William Agee since the battle ended late last September.

The fight with Bendix wasn't the only thing that has kept the normally quiet Martin Marietta in the spotlight recently. Debate over the future of two missile programs on which it is a key contractor--the MX and Pershing II--have raised questions about whether the company can count on the programs for future growth.

Pownall, who reiterated previous company statements that MartinMarietta has not based any long-range planning on the two programs, said he believes that the MX is being hurt by confusion over its basing mode, and predicted that Congress will approve the MX once the Reagan administration can explain the reasons for its "dense-pack" basing proposal. He also said the company hopes that a successful third test of the Pershing II--which has had one failure and one less-than-successful test firing--will help that project's future.

"Should those programs be by any chance terminated, then we'd be looking harder for other programs to fill in downstream," Pownall said.

"I don't want to belittle it, because they're two important programs to us," he added. "But I don't want to overemphasize the importance, either. We don't disappear as an aerospace company should either of these things or both go off line."

Analysts have been predicting the sale of the cement division, and perhaps other operations, since the Bendix battle concluded. Although results in Martin Marietta's aerospace operations have been strong--aided by several major government missile and aircraft contracts, including the MX and Pershing missiles--the company's other divisions did not fare quite so well in 1982.

Its aluminum division ran deeply in the red, and the cement unit lost a small amount of money as the result of two plant closings announced late in 1982.

Speculating on the sales and earnings outlook, Pownall predicted that "1983 looks to us as though it will perhaps improve modestly, and I don't know what 'modestly' means."