Alleco Inc., formerly Allegheny Beverage Corp., is in danger of defaulting on its debts because of this week's stock market mayhem.

Alleco said yesterday that Servam Corp. has not been able to obtain financing to buy Service America Corp., Alleco's food-service subsidiary, "because of the current unsettled financial market ... and is not in a position to commit to a closing date" for the sale. Servam had tentatively agreed to pay $450 million for Alleco's only remaining company.

Servam's financing arrangements for Service America fell prey to market forces this week because Servam's lenders were unable to finance the loan in the risky junk-bond market, according to sources close to the negotiations.

Although Servam has a commitment from the General Electric Credit Corp. to finance $400 million of the purchase, the agreement calls for GECC to finance only part of that on a long-term basis. Merrill Lynch is trying to arrange long-term financing by selling junk bonds. But, the market for those bonds is in disarray after this week's market plunge because many investors are shunning such high-risk investments.

If Alleco cannot sell Service America, it will be unable to make a $17 million credit payment due on Oct. 31. That default would trigger the recall of other outstanding bank loans and could force the company into bankruptcy.

A spokesman for Alleco said yesterday that the sale of Service America by the Oct. 31 deadline is "very uncertain," although Servam still wants to buy the firm and will continue to seek financing.

Alleco has asked its lenders for an extension on the due date of the $17 million loan payment. Although Alleco's banks have given no assurance of an extension, "Alleco believes that its lending group will be cooperative under the circumstances," according to a company statement.

Officials of Servam, which was formed by the New York investment banking firm of Morgan, Lewis, Githens & Ahn and senior management of Service America specifically to buy the Alleco subsidiary, could not be reached for comment yesterday.

Servam originally agreed to pay Alleco $500 million for Service America, but lowered the price to $450 million because of reduced profit projections for the company.

Shareholders would receive about $14 a share if the sale to Servam goes through. Alleco stock closed yesterday at $5.37, down $1.

Alleco officials have been trying for a year to sell Service America. The company has struggled under a burden of debt since purchasing the food-service company for $225 million in 1985 after selling its Allegheny Pepsi bottling subsidiary to PepsiCo.

Last week, Alleco and its chairman, Morton M. Lapides, were indicted in U.S. District Court in Norfolk on charges of price fixing. The charges were a result of a wide-ranging investigation of price-fixing in the beverage industry by the Department of Justice.