Told to get ready for bed, to clean up their rooms or to perform any other onerous task, small boys around the U.S. nowadays are likely to whip a plastic sword out of their He-Man brand pants and shout, "By the power of Grayskull, I have the power!" The incantation may not overwhelm parents. But when uttered daily on after-school TV by the hero of He-Man and the Masters of the Universe, it has proved puisant enough to capture the attention of more little boys than any other television show in America. He-Man power has sold $500 million in toys made by the Mattle Company for its Masters of the Universe line and anothe $500 million in He-Man toothbrushes, underwear, sheets and alarm clocks manufactured under license to Mattel.

It was Mattel in fact that originated the concept of an omnipotent He-Man in 1980 and sold the idea to Filmation, a Los Angeles-based production company. "We were trying to fill a hole in the marketplace," recalls Mattel President Glenn Hastings. "We looked at boys ages three to six and found that, unlike girls, they [liked] Good vs. Evil."

The formant devised as an upshot of this bit of pop-psych market research pits He-Man's Heroic Warriors against the forces of evil every weekday on 166 television stations. In each half-hour segment, He-Man starts out as a mere wimp of a kid named Adam. When he raises his sword and utters the magic incantation, Adam turns into a hero who looks like Prince Valiant with Arnold Schwarzenegger's physique. Since the animated cartoon premiered 15 months ago, it has gained 9 million viewers, most of them boys ages four to seven.

He-Man can zap his enemies with a vast array of weapons systems. Children can buy a He-Man doll astride a "heroic armored war horse" with two laser guns, or the skull-faced figure of Skeletor, the spirit of evil driving a circular "assault vehicle" equipped with rotating blades to slash the enemy. Should more conventional arms he needed, a handy Weapons Pak is available containing two miniature plastic pistols, a sword, an ax and a whip.

Despite all this armament, He-Man's producers point out that on-screen mayhem is held to a minimum. When the show was being developed. Filmation's educational consultant, Stanford University Communications Professor Donald Roberts, urged that none of the characters should get killed or "really hurt." In the midst of warfare, He-Man usually deplores violence. Thus, says Roberts, battle scenes are "really antibattle scenes."

Mattel and Filmation have so far kept He-Man an all-male preserve. But a new market will open up next fall, when Filmation begins airing its new series, She-Ra, Princess of Power. It will be the story of He-Man's twin sister, who leads a host of female warriors against an evil horde. Will she share in her brother's omnipotence? Not exactly. Producer Lou Scheimer explains that She-Ra is more caring than He-Man. "We tried to endow her with powers of nature rather than strength," he explains. "But she can do damn near anything that He-Man can."