NEW YORK (AP) _ Forbes Inc., the publisher of Forbes magazine, announced Tuesday that it had purchased American Heritage magazine, a leading general interest history publication.

Don Garson of Forbes Inc. said it was too early to say whether any changes were planned for American Heritage, which is published once every two months and has a circulation of about 150,000.

Forbes, which was the only magazine published by Forbes Inc., has a circulation of 720,000.

The sale included other assets of American Heritage Publishing Co., including its book division and a smaller magazine, American Heritage Magazine of Inventions and Technology, published three times a year. Terms of the sale were not announced.

''We are thrilled,'' Malcolm S. Forbes Jr., president of Forbes Inc., said in a statement. ''We have always felt an affinity for American Heritage. We have tremendous admiration for its tradition and excellence and look forward to building upon it.''

American Heritage won two National Magazine Awards in 1985 for general excellence and best single-topic issue.

Samuel P. Reed, the chairman of American Heritage Publishing Co. who headed a group of private investors that acquired the company in 1978, said in a statement: ''I'm delighted. I can't think of a better home for American Heritage than Forbes.''

The magazine was founded in 1954 under the sponsorship of the American Association for State and Local Historical Societies and the Society of American Historians. The latter group remains a sponsor, Garson said.

American Heritage has published articles by such authors as Bruce Catton, Barbara Tuchman, Henry Steele Commager, Arthur Schlesinger Jr., William Manchester and Theodore White.

Both magazines are headquartered in New York.