A congressional expert on the postal service warns that Americans within the next decade may have to stick a $1 stamp on each Christmas card or letter they mail.

Rep. Charles H. Wilson (D-Calif.) said yesterday that skyrocketing costs of the U.S. Postal Service could propel the price of the present 13-cent stamp to $1 within 10 years unless the semi-independent Postal Service agrees to accept additional subsidies from the taxpayer in a departure from their effort to operate on a pay-as-you-go basis.

Postal officials said yesterday that estimates made last year show that the price of a first-class stamp could go to 22 cents by 1982, and perhaps to 28 cents by 1985. "But there is no way under given current assumptions," a spokesman for the USPS said, "that it would ever get as high as $1 in 10 years . . ."

Wilson, a frequent critic of the postal establishment, chairs the postal personnel and modernization subcommittee of the House Post Office and Civil Service Committee. He and Rep. James M. Hanley (D-N.Y.) have introduced legislation that would alter the management of the USPS, now a government-owned corporation, making it more responsive to the President and Congress.

The Wilson-Hanley bill would replace the top management of the Postal Service, and return the selection of the Postmaster General to the President. The present board of governors would be abolished. And the USPS, which has been pursuing a policy of "break even" by increasing rates, would be given a subsidy equal to 15 per cent of each previous year's total budget. Currently that subsidy would be about $1.5 billion, or about the same amount the USPS now is running in the red Wilson says.

Wilson told a group of reporters that the Carter administration, which has been cool to his legislation, now is willing to discuss the plan. When the old Post Office Department was taken from the Cabinet in the early 1970s, it was with the understanding that it would be run as a business, with bonds sold and with rates adjusted to pay most operating costs.

USPS, which spends about 80 cents of every dollar it earns on labor costs, has negotiated two very generous contracts with unions representing most of its 600,000 rank-and-file workers. The last contract, a 3-year agreement that expires next July, included a no-layoff clause, improved fringe benefits and three guaranteed pay raises, plus six cost-of-living increases.

Unions begin negotiations with USPS in April. Many observers believe that a strike is inevitable if the USPS tries to hold down wage demands, or insists on removing the no-layoff clause. Postal plans call for reductions of employees to save money and elimination of many post offices. There also has been serious discussion of dropping Saturday mail delivery.

Some insiders predict the Carter Administration will try to bottle up the Hanley-Wilson bill in the Senate until the labor situation is settled in July. Wilson said yesterday that a majority of House members favors his bill, and it could clear that side of Congress by February or March.

Wilson also said postal officials will propose a total wage and fringe-benefit settlement of 6 per cent, in a two- or three-year contract. That figure is considered unacceptable to the powerful postal unions whose wildcat strike in March, 1970 led to creation of USPS. It caused a massive mail jam-up in the nation before President Nixon - with the help of Army troops - settled it.