The Social Security Act is being commemorated with a new 22-cent stamp coming out this Wednesday, 50 years to the day after it was signed into law.

The act, effecting a lasting revolution in American public policy, was for President Franklin D. Roosevelt the New Deal's "supreme achievement" and the "cornerstone" of his changes.

Of all the New Deal reforms, none dealt so comprehensively with the problem of the underprivileged, and this is reflected in the commemorative's design, which depicts the broad spectrum of Americans who benefit from Social Security.

The 1935 measure provided for federal-state unemployment insurance to cushion future depressions, for security in old age for workers retiring at 65 in specific categories with monthly pensions ranging from $10 to $85, for special categories of the needy, the aged, the blind, the disabled, dependent children and, through special grants to the states, for child health services, vocational rehabilitation and general public health.

Within five years of its enactment, about 28 million wage earners were entitled to unemployment insurance and about 46 million to retirement insurance.

The act has created an umbrella of protections, including old-age, survivor, disability and health insurance, compensation for unemployment, public assistance and health and welfare services. Because private pensions for employes in industry were the exception rather than the rule, the act brought millions under a retirement plan for the first time.

Today about 37 million persons receive Social Security benefits totaling more than $15 billion a month. About 122 million persons -- holding 95 percent of all jobs in the country -- are covered by Social Security.

The new 22-cent standard-size horizontal commemorative has as its framework the classic columns that appear on each side of the Social Security card held by millions of Americans; it is even of the same blue color. All text matter, the commemorative occasion and the postal data appear in an arch across the top that the columns hold up, similar to the designation on the real card.

Between the columns are seven silhouetted figures, three youngsters and four adults. A young boy holding the hand of an adult is at the left, a pigtailed girl pushes an elderly woman in a wheelchair in the center and a baby in a stroller is at the right. The two other adults are a man on a crutch with a foot in a cast and the mother pushing the stroller.

The stamp, designed by Robert Brangwyne of Boston, has been produced by gravure in shades of light and dark blue. There is a two-digit plate number per post office pane of 50 stamps along with the three usual marginal inscriptions.

The plate number is preceded by the letter "A," a designation used for stamps printed privately and not by the Bureau of Engraving and Printing.

Collectors of first-day-of-issue cancellations have a deadline of Sept. 13 -- orders must be postmarked by that date -- and the customary alternative ways of placing orders.

Collectors affixing stamps to their envelopes, which must bear addresses, should send their first-day covers to Customer-Affixed Envelopes, Social Security Act Stamp, Postmaster, Baltimore, Md. 21233-9991. No remittance is required.

Collectors preferring full processing by the Postal Service should send their covers, which must be addressed, to Social Security Act Stamp, Postmaster, Baltimore, Md. 21233-9992. The cost is 22 cents per stamp affixed to an envelope. Personal checks are accepted, cash is not welcomed, payment by stamps is rejected.