United Press International said yesterday that it has set Sept. 13 as the deadline for bids for the company and is asking for definitive acquisition proposals by early October.

The 78-year-old news service has been operating since April under Chapter 11 of the federal bankruptcy code and hopes to reorganize by finding a buyer.

UPI hopes the deadlines will "speed up the process" of finding a buyer by "providing a more formal structure," company spokesman William K. Adler said.

UPI has sent "confidentiality forms" to individuals and firms that have expressed interest in purchasing the Washington-based company, Chairman Luis Nogales said yesterday. Prospective buyers are asked to sign and return the forms as a way of agreeing to keep UPI's corporate information confidential.

Once the confidentiality forms are returned, UPI's investment adviser will send each prospective buyer a prospectus, detailing the company's financial condition and competitive strategy, Adler said.

The prospectus is "in the final stages of completion" and should be available next week, Nogales said.

After reviewing the document, each bidder must submit by Sept. 13 a prospective offer, including a preliminary price, the qualifications of the buyer and the proposed means of financing the sale.

UPI then will supply additional information and is "asking for definitive acquisition proposals to be in the investment adviser's hands by early October," Adler said.

The prospectus is not believed to include a suggested acquisition price.

UPI did not set a target date for concluding a sale, because any bid would have to be reviewed by the company's creditors and approved by the U.S. bankruptcy court.