CBS Entertainment announced yesterday that "News at Eleven," a TV movie starring Martin Sheen that gives an unflattering picture of local TV news operations, will air April 2 . . .

Sheen plays a San Diego anchor who tangles with his news director. That rascal is trying to boost the ratings by sensationalizing a story about sexual molestation charges pending against a junior high school teacher. The news director even wants to interview the "victims" before an indictment is brought in!!! (Never happen in real life, says Captain Airwaves) . . .

The network, whose affiliates can get sensitive about such things, took special pains with the script, which means the upright Sheen character will be given the opportunity to make several speeches on the public's right to know and the inherent rights of the individual . . .

A spokesman for CBS said yesterday that it was too early to detect any clearance problems from overly sensitive affiliates . . . e

Still another sign that Bill Moyers just may be running out his string at CBS News -- Elizabeth Karnes, his longtime aide and producer, is leaving to become special assistant to the president of Middlebury College . . .

For the last five years she has been an associate producer for Moyers. She first joined him 13 years ago when Bill was at PBS . . . She leaves in May . . .

And over at NBC News, there's talk that correspondent Lloyd Dobyns may be leaving the network after 14 years . . .

Assigned to the Tokyo bureau since October 1984, Dobyns is currently in New York completing work on the NBC White Paper "The Japan They Don't Talk About." The documentary explores the "dark side" of Japan's economic miracle and the vast social changes that miracle has caused. It airs April 22 . . .

Dobyns' contract is up in June . . .

An NBC News spokesman yesterday refused comment on the report of Dobyns' departure, saying only that "after the documentary is completed, we expect Lloyd to go through the normal management review process" (translation: It's in our mutual interest, Lloyd, to wind it up) . . .

Dobyns, one of the best writers in the business, has had an uneven career at NBC, marked by top-flight work on programs that earned at least two Peabodys and a duPont award for the network . . . He has also anchored several of NBC's magazine experiments, such as "First Camera," "Weekend" and "Monitor" . . . A couple of years ago, he and Linda Ellerbee coanchored the late-night "Overnight" program for a while . . .

Channel 56 says that starting this morning at 10 a.m. it plans to air, gavel-to-gavel, the 10 hours of House debate on aid to the contras (our latest word is that the debate is scheduled to begin at 3 p.m.) . . .

Which reminds us: Channel 5 conducted a nonscientific telephone poll on its 10 o'clock news Monday night on the question of aid to the contras. More than 9,000 callers voted, with 56 percent favoring aid . . .

"CBS Evening News With Dan Rather" continues to rule the network news race, compiling a 13.1 Nielsen rating and a 23 percent audience share for the week ending March 14. "NBC Nightly News With Tom Brokaw" was second at 12.4/22, "ABC World News Tonight With Peter Jennings" was third, at 12.0/21 . . .

Sportscaster Bernie Smilovitz bade farewell to his Channel 5 audiences last night as he headed for Detroit and the new job at WDIV . . .

Steve Buckhantz, weekend sportscaster for Five, will handle the weeknight chores for a while as WTTG continues to search for Bernie's replacement . . .

Part II of "If Tomorrow Comes" on CBS Monday night had a 23.6 national Nielsen rating and a 37 percent share of the audience. A repeat of "First Blood" on NBC over the same two hours did a 15.6/25 while "Triplecross" on ABC headed for the bottom of the charts with a 10.3/16 . . .

In development at CBS for the 1986-'87 season: a two-hour movie based on the all-time classic "Gunsmoke" series . . .

Already signed are Mister Dillon (James Arness) and Festus (Ken Curtis), and others from the original cast are expected to sign . . .

Oh Oh

Asheville, N.C., police have grounded Captain Cablevision (no relation), who had planned to wear a mask in the local St. Patrick's Day parade . . .

As Captain Airwaves could have told Captain Cablevision, it's against the law to wear a mask in public in North Carolina . . .

Cablevision is a pitchman for a cable TV company, who goes around wearing a cape as a cartoon law-and-order superhero . . .

Doug Benton, spokesman for Asheville Cablevision when he isn't playing Captain Cablevision, says that the Captain (the one in North Carolina) won't make any more public appearances until it's certain he isn't breaking the law . . .

Here's the weekend schedule for Channel 50, which is due to introduce a new programming lineup March 31 . . .

Saturday mornings begin with still-unspecified religious programming starting at 6 a.m. At 8 a.m., it's "Heckle and Jeckle," followed by "Lost in Space," Bowery Boys movies and a kung fu movie . . .

Starting at 1 p.m., it's a western movie followed by "Gunsmoke," "Rawhide" and wrestling . . .

At 6, it's "12 O'clock High," followed by "Space 1999," "It's a Living," "Check It Out," a sci-fi/chiller movie, "The Honeymooners" and a late movie . . .

On Sunday mornings it's religious programming until 8 a.m., followed by "Heckle and Jeckle," "Globetrotters," a Bowery Boys movie, a Laurel & Hardy movie, a Charlie Chan movie and two more movies . . .

"The John Wayne Threatre" airs at 5 p.m., followed by "Wild Kingdom," "Journey to Adventure," "Hee-Haw," "The Avengers," "Twilight Zone," "Check It Out," "Comedy Tonight" and religious programming . . .

And remember, WFTY will be carrying "The Goodwill Games" from Moscow in July . . .

TV Ratings

The situation comedy continues to dominate the schedule this season, so it's only fitting and proper that Comedy King NBC won the week with a 17.4 rating and a 28 percent audience share . . . taking Monday, Thursday and Saturday, where its sitcoms dominate . . .

CBS followed with a 15.7/25 for the week ending March 16, while ABC trailed with 14.2/22 . . .

In other results, NBC's "Family Ties Vacation" was 23rd, CBS' "People's Choice Awards" tied for 24th and ABC's "Between Two Women" was 29th . . .

David Copperfield's magic special on CBS was 33rd, the premiere of "Stingray" on NBC tied for 47th, the revamped "Redd Foxx Show" on ABC last Friday was 53rd, while CBS' new "Tough Cookies" was 59th . . .

"Benson" and "Fortune Dane" tied for 65th, to lead off the Final and Since They Were All on ABC Probably Fatal Five last week, followed by "He's the Mayor," "Ripley's Believe It or Not" and "Fall Guy," in 69th and last place . . .