The U.S. Postal Service's plan to increase the price of a first-class letter to 33 cents has run into a problem: The agency is making too much money. As a result, the independent postal rate commission, which must approve any increase, has suggested that the 32-cent stamp should stick around a bit longer. When the Postal Service's board of governors requested the one-cent increase on July 10, it was projecting that the agency would lose $2.4 billion in the current fiscal year. Thanks largely to the robust U.S. economy, the agency has continued to make money at a clip that has surprised some postal officials. It recorded a profit of nearly $1 billion in the first quarter of the current fiscal year, well ahead of its 1997 profits, and prompting revised projections that fiscal 1998 will be the agency's fourth year of $1 billion-plus in postal profits. The governors are to meet in the capital today.