US credit card lender American Express has unveiled plans to reduce its workforce by 10 percent in order to save $1.8 billion by the end of 2009.   Around 7000 jobs will be cut, mostly at management level or in areas which do not deal directly with customers. Amex also announced a recruitment freeze and the suspension of next year's management pay rises. Spending on travel, consulting and entertainment will also be cut.    Amex said the changes were necessary because of "the most challenging economic conditions in decades." Last week the company reported a 24 percent drop in third-quarter profit to $861 million. The proportion of bad debts written off by Amex has doubled from 3 percent last year to 6.1 percent.   Official figures released by the Commerce Department Thursday showed consumer spending had shrunk at an annual rate of 3.1 percent between July and September, the first contraction since 1991.    "The re-engineering program ... will also put us in a position to ramp-up investment spending as economic conditions improve," said Amex chairman and chief executive Kenneth Chenault.    However, the plans will cost the company up to $440 million in the fourth quarter, it said, mostly due to redundancy payments.    Amex said it also intends to reduce its budget for technology and marketing, so at least there may be less junk mail in our mailboxes.   *          *          *