Consumer default on credit card debt increased sharply this fall, according to a study of large pools of such "receivables," suggesting that the economic slowdown is draining individuals' pocketbooks and raising new concerns about banks that increasingly depend on consumers for profits.

The study by Moody's Investors Service Inc. of New York found that defaults in large pools of credit card debt jumped by more than 33 percent between the third quarter of 1989 and the same period this year. Defaults are accounts the lender has no hope of collecting.

Moody's looked only at debt that has been packaged into securities and sold, a market dominated by a few large banks. Spokesmen for Visa and MasterCard said their numbers for this year are somewhat lower than Moody's, but that the trend has been upward.

"It's a combination of factors," said Andrew Silver of Moody's. "The slowing economy is one. Another is the higher level of consumer debt that has accumulated and the increased competition in the bank credit card market."

Silver said that banks have issued cards faster than the market has grown, placing more and more credit at consumers' disposal.

A Moody's index showed defaults standing at 4.66 percent, compared with 3.31 percent in October 1989. Delinquencies -- bills 30 or more days overdue -- were 5.63 percent, up from 4.48 percent.

Visa International's delinquencies were 4.65 percent for this past quarter and 4.16 percent in 1989. MasterCard's were similar. "The delinquency trend for this year is upward," though not alarmingly so, said Richard Woods of MasterCard.

Moody's found a similar increase in the default rate among receivables from the three largest issuers of credit-card-backed securities. One of these is MBNA America Corp., the credit card subsidiary of troubled MNC Financial Inc. of Baltimore, which is also the parent of American Security Bank and Maryland National Bank.

MNC, which is struggling to pay off more than $820 million in long-term debt that is coming due over the next three months, has been trying to sell MBNA to raise cash. MNC had initially hoped to raise more than $1 billion from such a sale, but it has not been able to find a buyer and is now considering spinning the company off in a stock offering.

In its filing with the Securities and Exchange Commission related to that possible stock offering, MNC disclosed that its fraud losses on its credit card portfolio had more than doubled this year to $21.3 million. That, coupled with the Moody's report, suggests further problems for the big bank holding company in raising the amount it had hoped for from its credit card operation.

MNC officials did not return telephone calls seeking comment.

Bankers elsewhere, however, said that their credit card portfolios remain profitable and, while delinquencies are climbing somewhat, the increase is not out of line with what they expect in current economic conditions.