you just may not recognize it.

The familiar green punch cards issued by the U.S. government since the 1940s are being replaced by multicolored paper checks that are lighter, easier to store and more difficult to counterfeit. The first checks will be delivered to 20 million Social Security recipients today.

"This marks the start of a national conversion that will affect anyone who receives a government check," said Andy Montgomery of the Treasury Department's Financial Management Service.

About 600 million government checks are issued to 115 million Americans annually -- 500 million by the Treasury Department and the rest by non-Treasury dispersing offices, such as the Defense Department, Congress and the Tennessee Valley Authority.

Changeover costs for new equipment, printing and processing total $5 million, but the punch card technology and equipment are obsolete, Montgomery said. The lighter paper and reduced storage costs will save $6 million a year, he said.

The new government checks are the same size as the old ones but are printed in colors ranging from light blue to pale peach. They have an engraving of the Statue of Liberty on the front and the letters USA on the back.

Julie Ross of Henry J. Kaufman and Associates, primary contractor to the Treasury for public information on the conversion, said the new checks incorporate security features that make them difficult to alter or counterfeit:

*To prevent duplication, the USA in nonreproducible ink on the back of the check is invisible when microfilmed.

*An endorsement line on the check is composed of the tiny letters USA, which make it difficult to reproduce.

*When the new check is photocopied, the word "VOID" appears on the copy.

Ross said the check paper also will produce an obvious chemical reaction to mechanical erasures or ink eradicators. Stains will appear in the name of the payee or in the amount printed on the check if an attempt is made to alter those areas, she said.

The Financial Management Service has launched a public service campaign in print, on radio and on television to inform recipients of the change. Officials say they are pleased with the results. A pilot program in the Mid-Atlantic states distributed 200,000 Social Security checks in Philadelphia beginning in May. Hotlines took about 5,000 calls, but only about 25 were related to the new checks, and only two were from confused recipients.