The stock of Northwest Industries Inc. fell 6 5/8 to 48 1/4 yesterday following disclosure by the company that an investor group led by Chicago executive Donald P. Kelly is having difficulty obtaining financing for a proposed $1 billion leveraged buyout of the company.

The news surprised analysts and investors who believed Kelly's group would have little difficulty obtaining the necessary financing to complete the buyout. In an October interview with The Washington Post, Kelly said he had to turn away some investors who were interested in participating in the buyout of the Chicago-based conglomerate.

In a leveraged buyout, a public company is taken private by investors who finance the acquisition with borrowed funds, using the company's assets as collateral. The loans are repaid using cash generated by the company's operations or by selling assets.

In the proposed Northwest Industries buyout, Kelly had said about $800 million would come from banks and the rest from private investors. The announcement yesterday indicated the investor group is having difficulty raising the funds from private investors but did not explain why.

Analysts speculated that there may be a difference of opinion over what to do with Northwest's assets following completion of the buyout. They said some investors might favor selling almost all the assets, while others might be interested in retaining the company's subsidiaries.

Kelly's negotiations with investors are continuing, "but the purchasers are unable to predict the outcome" of the talks, Northwest Industries said yesterday. Kelly said last week that financing arrangements had not been completed but that he expected to have firm financing commitments before the end of the year.

Northwest Industries stock has traded between 62 1/4 and 40 7/8 in the last year. Analysts said yesterday that if the Kelly group does not come up with the financing, the stock could drop into the 40s again. If another buyer emerged, as anticipated, the stock's price would probably climb back into the 50s.

The investor group is led by Kelly, Briggs & Associates, a firm Kelly formed in August along with former Esmark Inc. vice chairman Roger T. Briggs. Oppenheimer Strategic Investments Inc. is also a partner in the group.

If Kelly can come up with the funds, this will be the third deal for approximately $1 billion each that he has completed in just over a year. He is the former chairman of Esmark Inc., a consumer products company that was acquired by Beatrice Cos. Inc. in August for $2.7 billion.

Kelly has said he would keep Northwest's most profitable subsidiary, Union Underwear Co., the company that makes Fruit of the Loom brand products. It is the subsidiary that makes the buyout worth doing from a financial point of view.

Kelly indicated he would sell Velsicol Chemical Corp., Northwest's troubled agricultural chemical subsidiary. All of the company's other operations would be closely reviewed before a decision was made about whether to keep them or sell them, Kelly said.

Northwest stockholders would receive $50 plus one share of Lone Star Steel stock for each share of Northwest they own, according to the terms of the leveraged buyout. Lone Star is a Northwest subsidiary that would be spun off to the public when the deal was completed.