General Motors Acceptance Corp., the finance arm of the world's largest car company, said it would buy Bank of New York's commercial credit business for $1.8 billion in cash in a bid to reduce GMAC's dependence on financing wholesale and retail vehicle purchases.

GMAC, which has been pursuing an aggressive diversification strategy for several years, will take over the bank's factoring business, which involves buying a company's accounts receivable and collecting payment on them.

Many consumers, whose credit-card or other commercial loans have been held by one company and sold to another, could be affected by GMAC's move into factoring.

GMAC may choose to insert advertising circulars into monthly bills, though those advertisements will not necessarily involve the marketing of cars and trucks, according to analysts familiar with GMAC.

The proposed sale, expected to be completed at the end of this month, would free the Bank of New York to concentrate on its more lucrative, fee-based business of handling securities transactions.

Officials at Bank of New York, the nation's 16th-largest bank, said their company will repurchase about 4 percent of its stock with an expected $1.05 billion pretax gain from its sale of BNY Financial Corp.

Automotive financing accounted for almost 75 percent of GMAC's net income of $1.33 billion in 1998. But GMAC also earned $226 million from insurance operations and $115 million from mortgage loans.

GMAC wants to improve those non-automotive earnings as a possible hedge against any downturn in hotly competitive car and truck sales, said David B. Healy, an Arizona-based analyst with Burnham Securities.

"Look at it as a modest diversification move, one that is aimed at making GMAC a little less dependent on the cyclical nature of car and truck sales," Healy said.

BNY Financial Corp., with 3,000 clients and $3.9 billion in assets, makes loans to North American and British companies having annual sales of $5 million and higher.

GMAC is one of the world's biggest finance companies, with $140 billion in auto, mortgage, credit-card and other loans.

The company's products also include insurance.

General Motors shares closed yesterday at $67.75, down $1.37 1/2, while Bank of New York shares rose $2.37 1/2 to close at $37.06 1/4.