* Amex cutting 6 percent of workforce

* Company "very cautious" about economy

* Shares edge lower after-hours (Adds details, spokesman comment, byline)

By Jonathan Stempel

NEW YORK, May 18 (Reuters) - American Express Co (AXP.N: Quote, Profile, Research), the credit card and travel services company, on Monday said it plans to eliminate 4,000 jobs, or 6 percent of its workforce, as the weakened economy causes higher customer defaults.

The cuts are part of the New York-based company's plan to save $800 million over the rest of 2009. They are in addition to 7,000 job cuts and an expected $1.8 billion of savings from a restructuring it announced in October.

Like many rivals, American Express has been hurt by rising delinquencies among cardholders, with the U.S. unemployment rate having risen to its highest level since 1983.

On Friday, American Express said its net charge-off rate, or debt it does not expect to be repaid, rose to 10.1 percent in April from 8.8 percent in March.

"We continue to be very cautious about the economic outlook," Chief Executive Kenneth Chenault said in a statement. He said the cost savings "will be reinvested in the business to make sure we can take competitive advantage of opportunities as the economy begins to rebound."