The Des Moines Register and Tribune Co., publisher of Iowa's largest daily newspaper, plans to hold a press conference today after directors meet to evaluate competing bids to purchase all or part of the company.

The announcement should end months of speculation about the future ownership of the company's most prestigious asset, The Des Moines Register, a newspaper with daily circulation throughout the state of about 240,000.

David Kruidenier, the company's chairman, said it is likely the company will announce the sale of some, but not all, of its assets, at the press conference.

Controversy regarding the disposition of one of the company's other highly publicized assets, a 14.3 percent block of stock of Cowles Media Co., publisher of the Minneapolis Star and Tribune newspaper, increased yesterday after Des Moines directors received a letter from a New York investment banking firm encouraging them to sell the stock to a single buyer, rather than distributing it to Register shareholders.

Bidding for The Register began Nov. 5 with a $112 million offer submitted by Dow Jones & Co., publisher of The Wall Street Journal, in association with two former Dow Jones employes who were then executives of The Register.

Potential buyers that have visited Des Moines recently include The Washington Post Co., The New York Times Co., Gannett Co. Inc., The Tribune Co. of Chicago, Morris Communications Corp., Cox Enterprises Inc. and Hearst Newspapers.

Lee Enterprises Inc., a Davenport, Iowa-based communications firm, confirmed yesterday it submitted a $105 million cash offer to purchase the newspaper. Lee President Lloyd Schermer said he made the offer even though he was not given access to the confidential financial information the other bidders received.

Schermer said The Register would not provide him with information he could use for competitive advantage. Lee owns Iowa newspapers that compete with The Register.

In addition to The Des Moines Register newspaper, The Register and Tribune Co. owns several smaller newspapers, the NBC television affiliate in Honolulu, the ABC television affiliate in Moline, Ill., four radio stations and 14.3 percent of Cowles Media Co.

Members of the Cowles family own most of the stock of the Des Moines company and of Cowles Media Co. Interfamily squabbles and complaints from shareholders about poor profits have led to pressure to sell one or both of the family companies.

Morgan Stanley & Co., the investment banking firm representing dissident Cowles shareholder Kingsley Murphy, said in a Jan. 28 letter to Register directors that major media companies are interested in acquiring the block of Cowles Media stock owned by The Register. The firm suggested that the stock should be combined with Murphy's 17.6 percent block and sold to a single buyer to maximize its value.

"In Morgan Stanley's view, such a block sale would achieve for your stockholders at least twice the market value realizable for the distributed shares . . . " the letter said.