Public hospitals are the subject of a new commemorative being issued Friday in New York.

The new 22-cent horizontal stamp is linked to the 250th anniversary of Bellevue Medical Center in Manhattan, which is the site of the first-day-of-issue ceremonies.

In America, a Philadelphia almshouse became the colonies' first public hospital in 1731. It eventually became known as Philadelphia General Hospital.

When Philadelphia General closed in 1977, Bellevue became the oldest continuing public hospital in the nation. Today, the Bellevue Medical Center, stretching over many city blocks and incorporating a range of facilities, is one of the largest hospitals in the country.

Bellevue came into being in 1736, when the House of Correction, Workhouse and Poorhouse opened with a six-bed infirmary. A century later it had grown to 5,000 beds with a main building and two wings. The predecessors of public hospitals were the public almshouses of 16th century England. Most of the religious institutions that provided help to the poor and sick were closed by Henry VIII when he broke with the Roman Catholic Church. Parliament enacted measures that placed the burden on local communities, which found themselves responsible not only for the sick but for the old, the homeless and the mentally ill.

All of these, along with petty criminals, were put into combination almshouses-workhouses.

The design of the stamp, created by Uldis Purins of Newton, Mass., is dominated by an abstract rendition of several floors of a modern hospital building with red and white trim in a blue sky. In front of the structure, on a green metal pole, is a blue and white service sign with a white "H." The commemorative designation and the postal data are in white.

The stamps have been produced by gravure in five colors: buff, brown, purple, blue and green. There is a five-digit plate on each post office pane of 50 stamps, preceded by the letter A. This letter precedes plate numbers of all stamps printed privately rather than by the Bureau of Engraving and Printing.

The new issue, like all other privately produced stamps to date, has been turned out by a joint venture of the American Bank Note Co. and J.W. Fergusson & Sons. It is the joint venture's fourth commemorative this year.

Collectors of first-day cancellations have a 30-day grace period from the day of issue to place their orders, which must be postmarked no later than May 11, and alternative ways of ordering.

Collectors who choose to affix stamps themselves on envelopes, which must bear return addresses, should send their first-day covers to Customer-Affixed Envelopes, Public Hospital Stamp, Postmaster, New York, N.Y. 10001-9991. No remittance is required.

Collectors preferring full processing of covers by the Postal Service should send their envelopes, which must be addressed, to Public Hospital Stamp, Postmaster, New York, N.Y. 10001-9992. The cost is 22 cents per stamp affixed on a cover. Personal checks are accepted, cash is not welcomed, payment by postage stamps is rejected.

Denmark has issued a 2.80-krone commemorative to mark the 25th anniversary of the founding of Amnesty International, the worldwide human rights organization working for the release of "prisoners of conscience." The multicolored issue depicts barbed wire entwined with flowers to symbolize the organization's nonviolent efforts for its causes.