Martin Marietta Corp. yesterday said it had reached an agreement in principle to sell its International Laser Systems subsidiary to Litton Industries Inc. for $46 million. The Bethesda company had said previously that the division was for sale.

Martin Marietta also said it was selling part of its real estate holdings in Orlando, Fla., to a Boston firm for $25 million.

The two moves are part of the company's continuing attempts to reduce its debt and clean up its balance sheet in the wake of last fall's takeover battle with Bendix Corp. Martin Marietta officials said at the company's annual shareholders meeting last week that the company has just about completed the program of pruning and consolidation, which has reduced the company's debt from $1.3 billion to about $800 million.

In another development, a Martin Marietta spokesman confirmed that the company is closing a computer center in Rosslyn and moving its data-processing services--which are offered to outside customers--to the company's large computer center in Orlando. About 45 employes are affected by the closing, which is scheduled for May 20. The spokesman said the closing was intended to cut costs and increase efficiency.

Martin Marietta has been increasing its stake in International Laser Systems since it first purchased a share of the unit in 1976. It currently owns 99 percent of the division, which makes laser systems primarily used in defense applications, such as targeting, as well as laser-based simulators and laser equipment for scientific and research use. The proposed sale of the division to Litton is subject to government approval.

The Orlando property being sold to Aldrich Eastman & Waltch Inc., a real estate investment firm, is part of Martin Marietta's large Orlando Central Park office and industrial park. The Boston company will acquire five office buildings in the transaction.

Martin Marietta acquired the Rosslyn data-processing center two years ago when it purchased some operations from American Data Systems, and the spokesman said the company had been phasing down the center's functions since it was acquired.

"What we really bought there was a customer base," he said, adding that closing and transferring the operations to Orlando "is a logical progression of taking over the customer base and expanding their service."

He said the company was attempting to transfer the employes affected by the Rosslyn closing, but one employe there said most workers were leaving the company. Martin Marietta is helping those leaving find new jobs, the employe said.