Fox Broadcasting Co., which recently took over the six Metromedia stations -- including Channel 5 here -- as the nucleus of a proposed "fourth network," is ending the operation of the national news bureau established by Metromedia in Washington . . .

A July 1 closing date is predicted . . .

Its operation will be consolidated with WTTG's local news unit, which will continue to furnish national coverage to the three other Fox stations -- in New York, Los Angeles and Houston -- currently airing local news shows . . .

Status of the nine members of the national bureau is uncertain at this time, although Fox Vice President Betty Endicott, who is in charge of both the bureau and WTTG news, said yesterday an effort will be made to absorb "some" of the nine at WTTG . . .

As it stands now, Fox stations in Chicago and Dallas have no local news operations at all and the immediate priority for the new network is to establish late-night and primetime programming schedules for what it hopes will eventually be at least a 70-station network of independent stations around the country . . .

The FCC definition of a "network" requires at least 15 hours of regularly scheduled programming a week to at least 25 affiliated stations in 10 states . . .

So far, Fox has announced "The Late Show With Joan Rivers" for airing at 11 p.m. week nights starting next fall and a primetime spinoff of the movie "Down and Out In Beverly Hills," 13 weeks of which are scheduled to begin next March . . .

Current speculation has FBC preparing a three-hour block of programming for one night starting in March, with another two-hour block premiering very shortly thereafter, specializing in movies, situation comedies and youth-oriented action dramas . . .

A full seven-night schedule is not expected to mature until at least 1990 . . . The current lineup of stations provides 21 percent coverage of U.S. TV homes. FBC hopes to have at least 85 percent coverage eventually . . .

The dispersal of the national bureau is the second trauma in recent years for that unit. Several years ago, Metromedia embarked on a big expansion of its activities. But as costs mounted, the project was suddenly abandoned and some 40 recently hired employes were drop . . .

The third outing of "West 57th" on CBS Wednesday night earned a 9.4 national Nielsen rating and a 16 percent audience . . . up from an 8.0/14 last week and, as long as we're letting it all hang out, an 8.0/13 the week before . . .

Also on CBS Wednesday night, "Stark: Mirror Image," up against the "Dynasty-Hotel" duo on ABC, got only an 11.0/18 . . .

Which reminds me . . . isn't that Ben Carrington a rat? . . .

Also on the magazine front, NBC's "1986" has brought in a consultant from the Entertainment side of the network . . . He's Ivan Fecan, vice president of creative affairs for NBC Productions . . . who is the go-between (he "liaises") for Brandon Tartikoff and the producer of the "Fast Copy" show for NBC . . .

And, since "Fast Copy" stories can sometimes spill into the news side of things, he also liaises with NBC News for the show . . .

"Fecan has a knack for packaging," according to one NBC executive. Ed Fouhy, executive producer of "1986 " says Fecan has been "helping us develop some things, mostly the theme music and some of our promos" . . .

Meanwhile, NBC met with Madison Avenue yesterday to show off the new fall schedule and "1986" received, an NBC source insisted, "a very positive reception" . . .

The show, which has undergone several metamorphoses since it was first launched to narrow acclaim last summer, "is much hipper, with lively segments and rock music," according to this unbiased source . . .

When "1986" coanchors Connie Chung and Roger Mudd had completed their presentation to the advertisers, Chung left them with . . . "As they say in Los Angeles -- trust us" . . .

By the way, among the story ideas hidden in the "1986" computer: a feature on "Second Bananas" -- like Larry (Bud) Melman, Ed McMahon -- and George Bush . . . plus a feature on the Washington Post Style section (comb your hair, Airwaves) . . .

Donald D. Wear Jr., a graduate of CBS Inc. in Washington (he ran the office here for three years), has been named senior vice president and general manager of CBS Broadcast International . . . responsible for all of the CBS/Broadcast Group's international program sales and marketing, videocassette and new venture activity, "which will be consolidated under the CBS Broadcast International banner" . . .

Wear has been vice president, policy, at Broadcast Group since 1985 . . .

William J. Small, former president of NBC News and a longtime top executive at CBS News, has been named director of the new Center for Communications at Fordham University, where he will also serve as Felix E. Larkin Professor of Communications . . .

Take it from old NBC and CBS hands, kids, there's a tough grader! . . . Also in the News

Tim brant, a graduate of Channel 7 here, has been named by ABC Sports to be college football game analyst, teaming with play-by-play veteran Keith Jackson for next season, replacing Frank Broyles . . .

The Corporation for Public Broadcasting board -- down to only five members as the Reagan administration takes its time with new appointments -- meets here today. It is expected to approve a budget of $202.2 million . . .

Also on the agenda: discussion of a television programming challenge fund, which would include a total CPB contribution of $12 million over the next three years, with a formula for PBS station matching contributions still to be worked out . . .

Election of a new general counsel has been postponed until a full 10-member board has been named . . .

So there! Both ABC and NBC insisted yesterday that despite CBS denials, CBS News did too bid on those phony Chernobyl nuclear accident pictures out of Italy, which ABC and NBC ran Monday but apologized for Wednesday . . .

In response, CBS News said late yesterday that, au contraire, they couldn't even find the chap who was working the scam to make the bid and, more than that, he even sent them a telex because he couldn't figure out the CBS phone number when he tried to contact them for a bid . . .

A 24-year-old Frenchman, Thomas Garenq, was arrested in Rome on charges of perpetrating the hoax. And on Another Front

Paul Duke, moderator of "Washington Week in Review" tomorrow will receive an honorary degree of doctor of humane letters "for distinguished contributions to journalism" from Centenary College in Hackettstown, N.J., where he will deliver the commencement address . . .

"Good Morning America" made a cross-country trip last week at a reported cost of $1 million to extol the pleasures of vacationing in terrorist-free North America . . .

In addition, ABC had the "North and South" mini-series in primetime, which conceivably could bolster morning numbers . . .

Nevertheless, for the week ending May 9, NBC's "Today" (which embarks on its own five day cruise Monday out of Wilmington, N.C.) won the morning network race for the 21st time in the past 22 weeks with a 5.3 Nielsen rating and a 25 percent audience share, compared with a 5.0/23 for "GMA" and a 3.3/15 for "CBS Morning News" . . .

Steve Friedman, executive producer of "Today" said yesterday, "I think their trip was a bust!" (sounds like Steve's mellowing) . . .