5 FRIDAY THE BROKAW REPORT: AMERICA THE VIOLENT (NBC, 8-9 p.m.) Tom Brokaw investigates the increasing use of guns by teens, the role of the media in fostering violence, and America's fascination with firearms.

6 SATURDAY

MYSTERY SCIENCE THEATER 3000 (Comedy Central, 7-9 p.m.) Joel and his robot pals begin a fourth season of B-movie send-ups. Tonight's turkey leftover: The delightfully dismal 1969 Space Travelers (a.k.a. Marooned), starring Gene Hackman, James Franciscus, Gregory Peck, and Richard Crenna.

DREAM ON (HBO, 10:30-11:30 p.m.; thereafter, Saturdays 10-10:30 p.m.) The third-season premiere episode finds this sitcom at its nimble best. Our hero- New York book editor, nice guy, and primo sap Martin Tupper (Brian Benben)- meets and beds a charming woman played by Teri Garr. A few days later, Martin finds his picture spread all over the front page of the New York Post- it turns out his one-night-stand-ee was the wife of a Senate candidate (he's played with slippery comic oiliness by George Hamilton). The show becomes a satire of recent political sex scandals, with real-life participants in such controversies-Gennifer Flowers, Rita Jenrette, and Jessica Hahn-making cameo appearances as TV reporters who grill Martin on his supposed sexual misconduct. As with the strongest Dream On shows, this special hour-long edition is full of funny jokes and even funnier throwaway lines; at one point, for instance, the ever-bronze Hamilton suddenly looks at the dress Garr is wearing and says petulantly, ''You're going to stand next to me at a press conference wearing green? You want those jaundice rumors to start up again?'' For her part, Garr is a slinky charmer; as a politician's wife, she wears her blond hair pulled back beneath a wide hairband-I don't think her sudden resemblance to Hillary Clinton is coincidental. By now, Benben has become an expert goofball, his face always collapsed in hapless befuddlement. His Martin is always hopeful that the next woman he meets will be the girl of his dreams, but by now, he's never surprised when she brings disappointment and trouble. Martin has become a first-rate TV creation, and Dream On a consistent pleasure. A

HOWIE MANDEL: HOWIE SPENT OUR SUMMER (Showtime, 10-11 p.m.) Comedian Howie Mandel played it relatively straight when he was impetuous Dr. Wayne Fiscus on St. Elsewhere, but his stand-up act contains lots of loony babble and crazy props: Think of Steve Martin's old stage routines and remove the wit, and you've got Howie.

The best thing about this special is that it offers a slightly toned-down Mandel-he's a lot easier to take. Summer is a pseudo-documentary about the comic's concert tour last summer. Chunks of performances from all over the country are interspersed with backstage footage that's supposed to be funny in an absurd way: Howie chatting with the eternally gold-chained Mr. T in a hotel room; Howie getting pointers from a veteran stage manager in the Catskills (he tells Mandel to ''always keep moving like Joel Grey''); Howie taking his road crew out for an overnight camping trip. None of it is very amusing, but Howie Spent Our Summer does prove that Mandel, who treats everyone with the same calm bemusement, isn't a complete jerk. C