Our Chateau Marmont Bureau Chief reports that on-air talent changes are pending for "Entertainment Tonight" . . . the syndicated Hollywood gossip show that airs at 7:30 weeknights on Channel 7 here. . .

Talk about your Unknowns, TV Column fans . . . Warner Bros. has picked Byron Cherry, 25, and Christopher Mayer, 28, to play Coy and Vance Duke . . . a couple of new "nephews" on CBS' "The Dukes of Hazzard" . . .

They will join the cast this morning as production for the fifth season of the series gets under way . . .

Although Paul Picard, executive producer of the series, announcing the newcomers last Friday . . . stressed that the additions of Cherry and Mayer were not "cast changes" and suggested "there's a possibility" missing costars John Schneider and Tom Wopat could still return . . . it's obvious that Warner's has now thrown its most powerful bargaining chip yet on the table in its two-month dispute with the absentees. . .

Cherry and Mayer were picked from 2,230 applicants ("hunks" is how a Warner Bros. spokesman aptly described them to a nevertheless shocked Captain Airwaves) interviewed around the country in June by the studio after Schneider and Wopat . . . who had played "Bo" and "Luke" on the series since the start . . . walked off the show and filed a $25 million suit against the producer . . .

They claimed that Warner Bros. had not given them a fair share of merchandising revenues earned on the side by the successful (third-ranked last season) series . . .

Warner Bros. promptly countersued for $90 million . . . denying the charges and claiming the company had been slandered by the departed costars . . .

At the same time, the nationwide "talent hunt" was launched . . .

The new nephews will make their first appearance the night of Oct. 1 when "Dukes" returns to its 8 p.m. Friday time slot for the fall season. . .

Cherry, from Buckhead, Ga., is described as blond-haired, blue-eyed, the youngest son of an architect and a former football player for East Tennessee State . . .

Mayer, according to Warner Bros., is the oldest of seven children of a machinery company sales manager in Ridgewood, N.J., and played rugby at Colgate, from which he graduated in economics . . . Moving Right Along

Local 31 of the National Association of Broadcast Employees and Technicians said Friday that the 15-member NABET unit at Howard University's WHMM-TV (Channel 32) has approved possible strike action . . .

NABET claims that University officials have refused to bargain after making changes in union work rules at the station . . .

No strike date has been set, as the NABET local hopes to get Howard to return to what one union official called "the status quo" . . .

Cameramen, switchers, videotape operators and other personnel are involved in the potential strike action . . . which a NABET official said was approved by "a nearly unanimous vote" . . .

CBS News correspondent Lem Tucker and the AFL-CIO have announced an out-of-court settlement of a suit arising from injuries Tucker suffered during the Solidarity Day rally here last September . . .

Tucker required hospitalization after a marshal, a member of the American Federation of State, County and Municipal Employees union, threw him to the ground during a scuffle as the correspondent attempted to approach the speakers' stand during the rally . . .

No details of the settlement were divulged . . . Wait, There's More

The Mobil Oil Corp. and ABC News have apparently reached a truce in a controversy that broke out when Mobil took exception to statements in a network documentary, "The Oil Game," which aired June 20 . . .

Ten days after the telecast . . . Mobil vice president Herbert Schmertz fired off a seven-page letter to ABC complaining of "prejudicial inaccuracies" suggesting that Mobil had been implicated in what introductory remarks at the start of the documentary called " . . . the biggest fraud ever committed against American consumers" . . .

Underlying the dispute was Mobil's refusal, during the year the documentary was being assembled, to talk to ABC unless the network permitted Mobil spokesmen to appear live and unedited on the program and allowed them to study Department of Energy documents being used by ABC . . .

In his June 30 letter . . . Schmertz specifically took exception to the program's claim that Mobil could pass on costs to its customers (through a "government bank") of a complicated deal in which it sold cheap crude oil to a company and subsequently purchased it back as more expensive foreign crude, meanwhile earning a $2.5 million "profit" on paper . . .

The "bank," Mobil pointed out to ABC, was the DOE's Entitlements Program, which was in existence in 1978 when the deal was made . . .

ABC News' "ombudsman," vice president George Watson, replied to Schmertz in his own four-page letter on July 14 . . .

Referring to Schmertz's three principal charges, Watson conceded that "there was no government bank as such" but claimed the "analogy" used in the program was a "clear and common sense way of transmitting complicated material to the lay public" . . .

Referring to "our statement that Mobil could pass on its costs to customers," Watson also said "we agree that this sentence could have been more precisely worded" . . .

Regarding the Schmertz charge that "the program stated or implied that Mobil was an integral part of the 'largest fraud' ever committed on the American public," Watson said that "in our view, this charge is not a fair or reasonable interpretation of what the program actually said . . .

"First of all," said Watson, "it is incorrect to assert that correspondent Dan Cordtz used the description in the segment dealing with Mobil's transactions. It was Democratic representative from Tennessee Albert Gore, not Mr. Cordtz, who made the 'largest fraud' charge, and he was quoted at the top of the program, not in the segment dealing with Mobil's transactions" . . .

Overall . . . Watson said, "We have carefully reviewed the program in light of your letter. It is our judgment that your charges are without merit and that, therefore, no corrective action is in order" . . .

Schmertz, on Friday, said that he is now satisfied that the phrase " 'largest fraud' did not and was not intended to apply to Mobil" and that the company "is delighted with that clarifcation . . . that was very important" . . .

"We're highly pleased that ABC has acknowledged the claim of inaccuracies noted in the show," said Schmertz . . . "even though it's clear that George is still saying he's right". . .

Schmertz said no further exchanges with the network are being considered but that an internal memo will be circulated to employes at Mobil detailing the ABC reply . . .

Meanwhile, said Schmertz, "we'll let the public decide" whether ABC was wrong . . .