NEW YORK (AP) _ Commodore International Ltd., the financially strapped home-computer maker, announced today that Thomas J. Rattigan had been promoted to chief executive, replacing Marshall Smith.

Rattigan, hired last year away from the chief executive post at Pepsico Bottling International, will take the helm of a company that has been hit by sluggish industry sales and price cutting.

Commodore, headquartered in West Chester, Pa., near Philadelphia, is pegging its hopes for revival on sales of its Amiga and Commodore 128 microcomputers. Sales of its older model, the Commodore 64, have slumped.

The company announced last month it had reached an agreement in principle with its major lending banks establishing a $135 million line of credit through March 15, 1987. The company had been in technical default for failing to comply with the terms of its agreements with major lenders.

Rattigan joined Commodore in April 1985 to head its North American operations and was promoted to president and chief operating officer in November.

Smith will remain on Commodore's board of directors and serve as a consultant to the company after Rattigan takes over as chief executive April 1, Irving Gould, the company's chairman, said in a news release.

Smith went to Commodore as president and chief executive in February 1984 and was named vice chairman in November 1985.

''With Thomas Rattigan's new appointment, Commodore is assured of a continuity of strong and decisive leadership,'' Gould said in the news release. ''This move completes the executive transition plan that has been in place since Mr. Rattigan joined the company.''

Gould praised Smith for ''tough decisions'' that he said had made Commodore competitive, and said he was instrumental in bringing Amiga Computer Inc. to Commodore.

Commodore reported a net loss of $53.2 million in the fourth quarter of 1985 in spite of posting sales that were the second highest in its history. The loss, on revenue of $339.2 million, compared with net income of $3.2 million in the same period a year earlier, when revenue was about 1 percent lower.

Most of the fourth-quarter loss came from a $29 million write-down against assets and a $22 million charge for the closing of two plants.

Security analysts have said Commodore's profit outlook remains cloudy, noting that the company has hired an investment banker to investigate further restructuring, which could result in more charges against earnings.