ABC takes another whack at the powerhouse CBS Friday night lineup tonight and lands, rather appropriately, on its keister. The network offers up two new series that should prove no threat to the competition nor to a viewer's powers of resistance: "At Ease," a derivative Army sitcom, at 8:30, and "The Renegades," a tedious update of "The Mod Squad," at 9, both on Channel 7.

David Naughton, once the nimble Pied Piper of Dr Pepper spots, and Jimmie "J.J." Walker, who ought to be on to better things than this by now, costar in "At Ease," which owes a lot to the Bill Murray movie hit "Stripes" but lacks any semblance of its appealing impudence. If there were a board game called "Sitcom," then "At Ease" would be the kind of show dreamed up by the loser. It was produced by Aaron Spelling and Douglas S. Cramer, doctors of drek both.

The characters are straight from stock, and the actors playing them generally overqualified: Richard Jaeckel as the hawkish Maj. Hawkins, who wears a G. Gordon Liddy wristwatch; Roger Bowen as the unit's ineffectual commanding officer, oh-so-wittily named Col. Clapp; semistarlet Jourdan Fremin as Cpl. Lola Grey; and John Vargas as Cardinel, Token Surly Hispanic, a cultural stereotype quickly gaining on Jivey Black Dude (as played by Walker) as television's weariest.

In the premiere, Walker and Naughton secretly arrange for a men's cologne commercial to be filmed on the base. Ron Landry and Tom Biener, who wrote the show, make the officers buffoons and the enlisted men crafty funsters, but their idea of a scam is an insult to the memory of Sgt. Bilko. Indeed, much of television today is an insult to the memory of Sgt. Bilko. Television insults memories right and left.

The memory of "The Mod Squad" may be hard to insult, but "The Renegades" gives it a snoozey try. Six muscular young men and one tough woman--a thug U.N. in miniature--work undercover for the cops on such cases as, tonight, chasing a tattered crop of mobster-gamblers out of local college sports. In the course of getting the goods on the bad guys, they say things like, "Take a leap, creep" and, "Eyeball this, turkey!" Perhaps that line should have been read, "Eyeball this turkey" in reference to the program itself.

ABC apparently tried to use Walter Hill's scintillatingly stylized urban gang movie, "The Warriors," in a radically altered version, as warm-up for its punk cops last week, but even "The Warriors" was a bust in the ratings, and "Renegades" looks oblivion-bound. The sole innovation is a zappy new scene-to-scene transitional gimmick that looks a little like a lightning bolt; kyooshhh, it goes. Saturday morning cartoons use similar devices, but more effectively. Besides, we have enough Friday night cartoons as it is.