Here is tonight's risk-free prescription for quality TV viewing: Take two "Seinfeld" episodes, one "Homicide" and one "Nightline." Then sleep well.
* "Mad About You" (8-9 p.m., WMAR, Channel 2) -- Cyndi Lauper may have had bad luck, and made some bad choices, when it came to accepting movie roles (and she has; remember "Vibes"?). However, she did fine when accepting a guest role on "Mad About You," as the freewheeling not-quite-ex-wife of Ira's. Like Annie Potts, she has a charismatic and natural way about her. The episode is a repeat and is the second of two "Mad About You" sitcoms shown in this kickoff hour. The first episode is an original, and has Jamie and Paul (Helen Hunt, Paul Reiser) trying to pull off a temporary "commuter marriage," working in different cities on different jobs and reuniting only on weekends. NBC.
* "Seinfeld" (9-10 p.m., WMAR, Channel 2) -- "Seinfeld," too, shows a pair of episodes tonight, but both are repeats, and both are from the stellar 1991 season. In the first, Kramer (Michael Richards) auditions for a Woody Allen movie; in the second, George (Jason Alexander) checks out a baldness cure. Both are VCR Alerts. NBC.
* "Herman's Head" (9:30-10 p.m., WBFF, Channel 45) -- Gilbert Gottfried -- who always! talks! like! THIS!!! -- is a guest star on, but not in, "Herman's Head" tonight. He plays a suicidal man on top of a building -- a depressed but funny guy with a roofless sense of humor. Fox.
* "Homicide: Life on the Street" (10-11 p.m., WMAR, Channel 2) -- The best TV news of 1994, so far, has been the great showing by last week's second-season premiere of "Homicide: Life on the Street," which wound up ranked No. 11 for the week. Here's hoping the momentum continues, and NBC realizes (just in time) the true value of this series. In tonight's episode, lines are drawn about what's right and legal in the investigation of certain cases, and "Homicide" surprises you (or me, anyway) by sometimes putting its detective characters on the "wrong" side of that line. Please watch this series; it's so good, I don't mind pleading. NBC.
* "Nightline" (11:30 p.m.-conclusion, WJZ, Channel 13) -- Ted Koppel has been on a career high this week, tagging around with Bill Clinton on his overseas summit and doing a nightly version of the election-eve special reports Koppel provided to ABC last fall. It gives the media term "public access" a whole new meaning: Koppel looks so comfortable around politics, and Clinton around Koppel, it makes these "Nightline" reports seem almost voyeuristic. ABC.
* "On the Beach" (10:15 p.m.-1:15 a.m., TNT) -- Consider this 1959 movie, based on Nevil Shute's nuclear-apocalypse novel, a sort of "The Day After: The Previous Generation." Gregory Peck, Ava Gardner star.