Robert Wagner returns to television, after all of two or three weeks away, as J.G. Culver, a crack insurance investigator for a crack insurance company in ABC's "Lime Street," premiering at 9:30 tonight on Channel 7 and thereafter airing Saturdays at 9, until such time as it mercifully falls through the cracks. There's a special quiet corner of oblivion waiting for this one.

Wagner is pudgily befuddled in the lead role, wandering through the program like a transient in a strange bus terminal, infecting the whole enterprise (it is "an R.J. Production," meaning his company did it) with a wearily Wagnerian torpor. This program might be just the thing to empty a mind prior to inducement of a hypnotic state.

Samantha Smith, pen pal to Yuri Andropov, died in a tragic plane crash after completing five episodes of the series in the role of Culver's oldest daughter. From all appearances, she took to acting like a natural. ABC said that tonight's 90-minute premiere, although screened for the press last June in Los Angeles, was unavailable for preview, so next week's episode was screened instead. Smith is featured prominently and to good effect.

But the whole production has the playful buoyancy of cement and the zippity pace of August. Wagner finds a like-minded cohort in John Standing, who plays his British colleague; the firm is based in London and the two are supposed to have been classmates at Oxford, ha ha ha ha ha. Standing plays the part in that fussy-prissy way British valets are usually played. Lew Ayres, as Culver's father, looks as though he can't wait to hear the word "cut!" And who could blame him?

Next week's program deals with a faked plane hijacking investigated by Culver, who is never in the slightest jeopardy until the last few minutes, when his boat chases a plane up the Potomac River. As usual in a crime show, the hero inhabits a kind of Third World of law enforcement; crooks are depicted as unsavory, but so is an agent of the FBI. It's that old you-can't-trust-anybody baloney that only serves to remind a viewer of the obvious: You can't trust television.