The Christian Broadcasting Network confirms that it is considering selling WYAH-TV (Channel 27), its flagship station in Portsmouth, Va. . . .

A TV broker has estimated that the station could be worth about $7 million on the market . . .

Financial arrangements are apparently near completion and so it is now almost certain that the highly regarded "MacNeil/Lehrer Report" will expand to a full hour on week nights sometime in 1983 . . . It hasn't been easy assembling underwriters out in the shrinking world of public TV donors, since the current $7 million annual budget for the half-hour version of "MacNeil/Lehrer" will jump to about $18 million for a full schedule of the hour show, five nights a week, sources say . . .

Executives at coproducing stations WNET in New York and WETA here now plan to get the expanded "Report" on the air by July of next year so it can work the kinks out by the fall, when bigger TV audiences will be available on PBS stations around the country . . .

And a couple of more public TV notes: Luciano Pavarotti will sing the title role in Mozart's "Idomeneo" . . . which will be seen Jan. 26, 1983, "Live From The Met". . .

And that three-part documentary, "Saudi Arabia," actually out-pulled top PBS entertainment series during the May ratings sweeps . . . at least in the five metered Nielsen markets the public network polls for research purposes--New York, Los Angeles, Chicago, Philadelphia and San Francisco . .

The "Saudi Arabia" average for those five markets, the biggest in the country, was a 4.3 Nielsen and a 7 percent audience share . . . numbers which PBS officials here say are "very high for a public affairs show, particularly documentaries" . . .

"Saudi Arabia" was a joint production of Pacific Productions here and the Pacific Mountain Network, a group of 32 regional public TV stations in the West . . .

Although there was a brief flurry of criticism preceding the telecasts, at a time when Israeli-Arab relations were particularly poor, the series generally received acclaim from TV writers around the country . . . and WNET in New York reported large audiences . . .

The three-parter's success has PBS looking for more documentaries that try to give a balanced view of some of the less-publicized areas of the globe . . .

Channel 9 has launched a nationwide search for a new host for "Saturday Magazine," following the death of Steve Douglas in a light aircraft accident earlier this summer . . .

Weekday anchor J.C. Hayward will continue to fill in as host pending results of the search . . .