A weak U.S. labor market led to bigger bank writedowns of credit card debt in August as a record-high jobless rate left consumers struggling to pay their bills.

Charge-offs, or the writedown of uncollectible debt by banks, increased 81 basis points to 10.62 percent in August, after a 31 basis points decline to 9.81 percent in July. On the retail front, credit card writedowns increased 49 basis points to 9.99 percent in August, according to JPMorgan Securities.

Citibank posted the biggest credit card losses in August, with charge-offs climbing to 12.14 percent from July's 10.03 percent, it said.

On a positive note, however, American Express, Capital One and National City posted lower charge-off rates in August with declines of 44 basis points, 20 basis points and 24 basis points, respectively, versus the prior month.

Losses in securities backed by credit cards generally track increases in the unemployment rate. The jobless rate hit a 26-year high at 9.7 percent in August.

JPMorgan expects to see further credit card ABS deterioration given the still weakening labor market and projects charge-offs will reach an 11 to 12 percent range as unemployment climbs above 10 percent in 2010.

However, it said the outlook for fundamentals over the longer term remains positive, as a peak in unemployment and a recovery in the broader economy remain in sight.

In addition, it said the ongoing support and maintenance by issuers of their credit card portfolios along with built in structural protections in ABS transactions should remain more than adequate to absorb the higher losses.

JPMorgan maintains an 'Overweight' on credit card ABS and recommends a move down in credit, as overwhelming demand relative to the supply of top-rated securities, pushes spreads even tighter.

Three-year AAA-rated credit card securities now trade at a leaner 75 basis points spread over Libor, in dramatically from their record wide 550 basis points spread level set in late 2008 during the height of a credit crisis.

(Reporting by Nancy Leinfuss; Editing by Kenneth Barry)