The stamps bear an official portrait of the royal couple. The 14p has a background of blue and the 25p has a background of beige. Both the Prince and his lady are facing the camera with the half smile that seems to be de rigeur for engaged couples.

Running up from the bottom in a tucked-away spot along the left side is ''29 July 1981.'' Aside from the denomination, that date is the only lettering on the stamp. The name of the issuing country never appears on the stamps of Britain, a practice going back to the invention of the first adhesive postage stamps by Sir Rowland Hill in 1840.

Beginning with the world's first stamps, the Penny Black and the Twopenny Blue that bore the head of Queen Victoria, Britain has always considered the head of the sovereign to be sufficient identification. No other country has ever tried to emulate Britain.

The absence of the country's name has been helpful to British designers, who traditionally prefer to keep lettering to the barest essential. There is not likely to be anyone in the British Isles, or in the entire world - much of which was once in the British Empire and remains linked by British Commonwealth ties - who would have to be told who the two young people on the stamps are.

The traditional silhouette of Prince Charles' mother, Queen Elizabeth II, appears in the upper right corner of the stamps. The presence of the silhouette caused the official portrait to receive far more publicity than such portraits for posterity usually get. The portrait shows the tip of Lady Diana's head barely reaching up to the Prince's chin, making him appear virtually a head taller. Newsmen who had seen the royal couple in public on a number of occasions were baffled because the royal couple they had seen were virtually of equal height.