As a sure-fire ratings-getter, the season-ending cliffhangers for primetime soap operas ain't what they used to be . . .

Last Thursday, the networks wrapped up the cliffhanger season with the finales of "The Colbys" on ABC and "Falcon Crest" on CBS . . . and neither series matched its weekly average audience over the just-completed season . . .

"Colbys" drew a 15.9 Nielsen average and a 26 percent audience share, which means the finale was seen in 86,000 fewer TV homes than on an average week -- when it attracted 13.7 million homes . . .

The earthquake on "Falcon Crest" was seen in 171,900 fewer homes than the show's weekly average of 15.5 million . . .

Actually, only CBS' "Dallas," among the nighttime soaps this year, managed to attract a real mob (2.5 million extra TV homes over its weekly average of 18.8 million) with its cliffhanger . . .

There were two other mini-successes this month. On May 15, the finale of CBS' "Knots Landing" managed to pick up 430,000 homes over its weekly average of 16.7 million homes. That same evening, a kind of cliffhanger on NBC's final "Cheers" was 601,000 homes over the show's 20.3 million season average . . .

But ABC's "Dynasty" on May 21 was only 86,000 homes over its 18.7 million average; and on May 7, poor old "St. Elsewhere" on NBC was down 1.1 million from its weekly average of 11.8 million for its cliffhanger . . .

Despite filing a $10 million suit alleging racial and sex discrimination against Channel 7 last week, Assistant News Director Penny Mickelbury will continue on the job at WJLA, according to Executive News Director Tom Doerr . . .

Mickelbury is in charge of all specialty units, anchor projects and planning for the news operation . . .

The suit, filed in D.C. Superior Court, charges that the station passed over Mickelbury for promotions as "part of a pattern and practice of discrimination against black employes at WJLA-TV," a charge denied by Thomas Cookerly, WJLA president and general manager . . .

He said Friday the station "is proud of our record in minority hiring. We rank in the top 5 percent in the country in minority hiring" . . .

Mickelbury seeks $5 million in compensatory damages and $5 million in punitive damages. Named in the suit are the station; its parent, Allbritton Communications; Cookerly; and Doerr . . .

Mickelbury charged that Doerr, who had been working as news director for the Allbritton station in Tulsa when he was named to the WJLA job in October 1985, was "preselected" in secret for the new position of executive news director, even though he had, the suit claims, "substantially less experience" than Mickelbury. For three months in 1984, Mickelbury served as acting news director at the station . . .

The suit charges violation of the 1977 D.C. Civil Rights Act as well as U.S. civil rights statutes . . .

Mickelbury was not available for comment yesterday. Doerr declined comment on the pending suit . . . Another Subject

Doerr, however, was eager to talk -- about the news ratings so far in the May sweeps . . .

According to Doerr, Nielsen figures for Monday-Friday through May 21 indicate Seven news is second behind Nine at both 5 p.m. and 6, but running third at 11 p.m. behind Nine and Four . . .

In Arbitron, according to Doerr, Seven leads at 5 p.m., is second at 6 p.m. and leads at 11 p.m., with Four ahead of Nine at that hour . . .

Incidentally, rivals have complained that Nine recently conducted an audience study that asked 500 to 600 viewers surveyed by telephone to watch the station for three nights, after which they'd be called back for questioning . . .

A Nine official Friday said parent Gannett instituted such a study just before the May sweeps, which "might" have run over a couple of days, but that Nielsen -- which frowns on the practice during a sweeps month -- "was satisfied" that the brief overrun did not affect the ratings (the chances of a random telephone poll tracking across Nielsen homes are considered slim) . . .

(Captain Airwaves just wishes some survey had called him Thursday night when Nine ran a crawl during the climax of "Falcon Crest" hyping an upcoming 11 p.m. news story. He'd have given them an earful!) . . .

Larry Shainman, who has been a reporter at Channel 4 since 1980, is leaving to become press secretary to Sen. Nancy Landon Kassebaum (R-Kan.)

Shainman, who came to WRC from NBC-owned WKYC in Cleveland, asked out of his contract to accept the job, which he begins in June . . .

Talk is strong in New York that ABC News -- despite recent cutbacks -- just may add five correspondents to the roster during the summer and is t-h-a-t close to naming a woman to be a senior producer on "ABC World News Tonight With Peter Jennings" . . .

CBS News correspondent Bill Moyers will interview U.S. Supreme Court Chief Justice Warren Burger sometime in June for a one-hour program later this summer marking the bicentennial of the U.S. Constitution . . .

Hearings are now expected in mid-July before the Senate Commerce, Science and Transportation subcommittee on communications on a bill submitted earlier this year by Sen. Dale Bumpers (D-Ark.) called the Rural Satellite Dish Owners Protection Act . . .

The bill calls for the industry to set a reasonable price for and make readily available to consumers standardized decoders enabling dish owners to pick up scrambled TV signals . . .

Bumpers has considered a call for a moratorium on signal scrambling . . .

And on June 12, the House subcommittee on telecommunications, consumer protection and finance will hold its second satellite scrambling hearing . . .

Rep. Tim Wirth (D-Colo.), subcommittee chairman, said witnesses will include Thomas Evans, chairman of the Rural Satellite Dish Owners Association, in Rye, Colo.; Randy Winegard, a Dubuque, Iowa, manufacturer of satellite dishes; William A. Ternent, vice president of American Technology and Information Inc. of Denver; Mark Fowler, chairman of the Federal Communications Commission . . . plus representatives of the TV networks, and the cable and motion picture industries . . .

The hearing will also look at the impact on the communications industry of the late-April "Captain Midnight" incident, in which someone illegally used a powerful transmitter to interrupt HBO's programming . . .

Hal Levenson, formerly of Metromedia and most recently senior producer of the PBS religious news program "News Front," has been named news director of WAVY, the NBC affiliate in Norfolk . . .

CBS News correspondent Lem Tucker will be graduation speaker for the Duke Ellington School of the Arts commencement exercises to be held at the school this Friday . . .

Now that we know ABC will repeat Herman Wouk's 18-hour mini-series "Winds of War" over six nights in early September, we learn that Robert Mitchum has signed to repeat his "Winds" role as Pug Henry in the 30-hour sequel, "War and Remembrance." Hart Bochner will play Byron Henry, Jane Seymour will be Natalie Jastrow Henry (replacing Ali MacGraw), and Sir John Gielgud will play Aaron Jastrow . . .

And to prepare us for the "Miami Vice" vs. "Dallas" contest at 9 p.m. Fridays starting this fall, NBC will put "Miami Vice" reruns at that hour against "Dallas" reruns starting June 6. "Vice" will be a lead-in to 10 p.m. reruns of "Stingray," which has already been selected to come back as a replacement for some faltering series next fall . . .