Three gaunt faces of hunger appear on a new U.S. stamp coming out Tuesday. The faces symbolize the plight of millions suffering from hunger throughout much of the world.

The stamp is being put out in Washington with a first-day ceremony at the Rayburn House Office Building at 9 a.m. Rep. Mickey Leland (D-Tex.), chairman of the House Select Committee on Hunger and an ardent supporter of the stamp, will take part, along with Postmaster General Paul Carlin.

Below the faces is the theme "Help End Hunger," an upbeat change from the original choice, "Combat Hunger," which was made to suggest that the war against hunger can be won, perhaps even by the end of this century.

United Nations experts estimate that more than 500 million persons are without enough food throughout the world. In Africa alone, more than 150 million adults and children are at risk of starving to death. Millions in India and Bangladesh exist on a starvation diet.

Modern technology has made possible such agricultural improvements as high-yield crops, more efficient irrigation and new sources of food, but poverty, politics, ignorance, farmland becoming desert and other factors have kept many Third World countries from utilizing them, and these nations remain incapable of feeding their own people.

Consequently, many organizations such as the Peace Corps and the U.N. Food and Agricultural Organization have initiated far-reaching programs to reduce food and crop losses from disease and pests.

Private concerned groups such as The Hunger Project, End Hunger Network and U.S.A. for Africa have had notable success in generating millions of dollars in donations and arousing considerable public support for efforts to end world hunger.

The 22-cent horizontal stamp in the standard commemorative size was designed by Jerry Pinkney, an artist from Croton-on-Hudson, N.Y. It has been produced by gravure in five colors: yellow, magenta, cyan, black and black line. There is a five-digit plate number per post office pane of 50 stamps. The plate number is preceded by the letter "A," indicating that it has been privately produced under contract with the Postal Service.

Collectors of first-day-of-issue cancellations have the usual 30-day grace period from the date of issue to place their orders, which must be postmarked no later than Nov. 15, and alternative ways of ordering.

Collectors acquiring stamps themselves and affixing them on their envelopes, which must be addressed, should send their first-day covers to Customer-Affixed Envelopes, Help End Hunger Stamp, Postmaster, Washington, D.C. 20066-9991. No remittance is required.

Collectors preferring full processing by the Postal Service should send their covers, each addressed, to Help End Hunger Stamp, Postmaster, Washington, D.C. 20066-9992. The cost is 22 cents per stamp affixed on an envelope. Personal checks are accepted, cash is not wel-comed, payment by postage stamps is rejected.

The inspiration for the stamp came from Phyllis Alroy, a volunteer for The Hunger Project, two years ago. She was able to enlist Leland's backing. She also won the support of many other volunteers in the organization, which at present has a membership of more than 3.5 million from 152 countries.

The volunteers gathered more than 100,000 signatures from persons all over the United States in support of Alroy's proposal, which went to the postmaster general and the Citizens Stamp Advisory Committee.