* American Express Co. reported improved fourth-quarter...

* American Express Co. reported improved fourth-quarter and full-year profits from a dismal 1990. But the results reflected recession-related problems at its card and travel services division.

The 142-year-old company known for its green, platinum and gold charge cards reported earnings of $237 million, or 47 cents per share in the last three months of 1991, up from $138 million, or 28 cents per share, a year earlier. Revenue was $6.63 billion, up 5.1% from $6.30 billion a year earlier.

For the year, American Express reported profits of $789 million, or $1.59 per share, up from $181 million, or 34 cents per share. American Express’ 1990 results reflected a loss of nearly $1 billion at its Shearson Lehman Bros. brokerage unit.

Total 1991 revenues rose 5.9% to $25.8 billion from $24.3 billion.

But analysts said the results by division reflected major difficulties. They cited lower-than-expected earnings by its Shearson Lehman Bros. brokerage unit, whose profits fell far short of its Wall Street competitors in a booming year.

At its main travel related services unit, American Express reported large provisions for credit losses, increased expenses and advertising costs, and only a slight increase in revenue.

American Express said TRS, which includes its charge card, Optima credit card and travelers checks, tumbled in the fourth quarter to $81 million from $215 million a year ago.