From the techno-wizards who brought us Late Night With David Letterman's thrill cam and Las Vegas showgirl cam comes (drum roll, please)... helmet cam. The tiny camera, which offers a quarterback's-eye view of the football field, made its debut late last month on the USA Network during a World League of American Football game. Orlando Thunder quarterback Kerwin Bell, who wore the two-pound device (consisting of a lipstick tube-size camera in the helmet's padding wired to a battery pack and transmitting device in his shoulder pads), says it was not only comfortable but survived ''four or five of the hardest hits'' he'd ever taken. What's more, the new camera can give fans a true picture of game action. Helmet cam offers ''armchair quarterbacks the chance to see exactly what we see and realize receivers don't look as open as [viewers] think,'' Bell says. They must have been fairly open for him, though; Bell threw five touchdown passes in his team's 35-34 victory over the San Antonio Riders. Indeed, the helmet cam was a window on a sometimes dizzying array of plays, including the thundering rush of defensive linemen. But the camera's angle, framed within the helmet, lends a fun-house-mirror quality to the play. It also ''adds some comic relief when the quarterback goes down, you just see grass and legs,'' says Craig Janoff, the USA Network's executive director of World League coverage. Janoff, who hired California-based Aerial Video Systems to create the device, also directs ABC's Monday Night Football. So far, neither the NFL nor David Letterman has expressed interest in the unit.