To the vast -- if unspoken -- relief of programming executives and ad salesmen at CBS and NBC, the White House yesterday announced that President Reagan will deliver his State of the Union address next Tuesday at 8 p.m., instead of 9 p.m., as originally planned . . .
As a result, CBS will be able to air the conclusion of its mini-series "Sins" as first scheduled, at 9 p.m. that night. Likewise, NBC will broadcast part III of its "Peter the Great" mini-series at 9, also as originally scheduled . . .
In a statement that carried no explanation, the White House Press Office announced the time change, which came two days after Reagan postponed the speech by a week due to the loss of the space shuttle Challenger earlier Tuesday . . .
If the 9 p.m. start time for the presidential address before Congress had remained, both CBS and NBC would have faced the problem of delaying until 10 p.m. the start of their expensive mini-series episodes, a late start that could lower viewership and TV commercial revenues -- often based on audience delivery guarantees . . .
The president's address is expected to be shorter than usual, about 20 minutes. It will be followed by a Democratic response of similar length, which all three networks are expected to carry . . .
As it stands now, CBS will begin "Sins" at 9 p.m., preempting "Charlie & Co." and "Melba" between 8 and 9. NBC will preempt "The A-Team" that night, starting "Peter the Great" as scheduled, at 9 p.m. . . .
ABC, which was sticking to its popular Tuesday night regular schedule that evening, anyway, to compete with the two mini-series, yesterday announced it will drop "Who's the Boss?" and "Growing Pains" from the Feb. 4 lineup . . .
The White House earlier yesterday had asked Congress to revise its joint resolution inviting the president to address the House and Senate, reflecting the time change . . .
By late yesterday, the House had voted in favor of the change with similar Senate action expected either late Thursday or today . . .
Both CBS and NBC on Wednesday had reacted with some asperity to rumors they were "pressuring" the White House to rethink its 9 p.m. speech time . . . a notion that also amused White House spokesman Larry Speakes . . .
Speakes acknowledged, however, that in the case of most presidential TV appearances -- short of a major address like the State of the Union -- the White House has taken into consideration possible network conflicts . . .
"It was just decided we would prefer to do it at 8 o'clock rather than 9 o'clock," deputy White House press secretary Albert Brashear told United Press International . . . TCBS Plans Trip
To probe the nation's farm crisis, "CBS Evening News With Dan Rather" will spend the week of Feb. 24 in Sun Belt and Upper Middle West farm country . . .
Monday and Tuesday of that week, the program will broadcast from KENS-TV, the CBS affiliate in San Antonio, Tex. The next three nights, "Evening News" will originate from KELO, in Sioux Falls, S.D. . . .
Lane Venardos, executive producer of "CBS Evening News," said yesterday that network research has determined that the farm crisis will be one of the continuing big stories of 1986 . . .
As for the choice of the week of Feb. 24, Vernardos said "that's the week that spring planting actually begins in most of that part of the country. And the week before, we've been told, 65,000 foreclosure notices will be going out to small farmers all over the country, mostly in the Midwest. Now that's a major domestic story -- the worst year ever for the small farmer. And it will be a continuing story" . . .
Venardos said a good deal of advance shooting is planned and there "will be heavy involvement by Dan" . . .
During that week a major part of each nightly broadcast will be devoted to the farm crisis story, Venardos said, but he declined to venture any percentage figure on each program . . .
Venardos denied the farm trip was in response to the week-long visit to Moscow the same week by "ABC World News Tonight With Peter Jennings," which will focus on the Soviet Party Congress . . . a notion that yesterday crossed the minds of several at ABC News . . .
"We'll have full coverage from top people like Tom Fenton and Bernie Goldberg of the party congress that week," said Venardos. "And remember there aren't that many stories you are allowed to work on in Moscow that can fill a whole week" . . .
"NBC Nightly News With Tom Brokaw" will be staying in New York that week (which also happens to include the end of the February ratings sweeps). Brokaw recently returned from South America and during the week of Feb. 10 his reports from Argentina, Brazil, Peru and Chile will air nightly . . .
NBC News' reaction to the Rather trip was a small yawn, accompanied by even smaller jokes about Dan's venture into "Brokaw Country." Brokaw was born in Yankton, S.D. . . . Also in the News
Erin Moriarty, who has been a consumer reporter at WMAQ, the NBC-owned station in Chicago, has signed to be consumer reporter for "CBS Morning News," starting in mid-February . . .
Moriarty, who is an attorney, replaces Betsy Ashton, who has been on occasional loan from WCBS in New York, where she's the regular consumer reporter . . .
Charles Gibson, who covers the House for ABC News and is backup numero uno for Ted Koppel on "Nightline," has signed a new four-year contract, which, because negotiations went on for so long, is really for only three years . . .
Both Moriarty and Gibson are represented by agent Cynthia Riley. Captain Airwaves promised to put her name in the story because in three previous TV Column items about Cynthia Riley, he's never spelled her last name correctly . . .
Brian Williams, who has been a reporter at Channel 5 the past three years, is leaving as of tonight's broadcast to become New Jersey correspondent for WCAU, the CBS-owned station in Philadelphia . . .
Williams' agent is Steve Dickstein of Philadelphia, who also happens to represent WDVM's Glenn Brenner . . .
Those folks at "Today" are going to be impossible to live with if this keeps up . . .
For the week ending Jan. 24, the NBC show led the early morning network race with a fat (for early morning, anyway) 5.8 Nielsen rating and a 25 percent audience share . . . compared with a 4.6/20 for ABC's "Good Morning America" and a 3.2/14 for "CBS Morning News" . . .
For "Today," that's 1) the highest rating since the week of Jan. 11, 1982; 2) the first time the show has had a five-point rating lead over anybody since the week of May 21, 1979; and 3) the biggest ratings margin (1.2) over GMA since the week of Dec. 18, 1978 . . .
Speaking of ratings, "Dynasty" continued to make a comeback Wednesday night, racking up a 23.9 rating and a 34 share in the quickie national Nielsens . . .
Last week a 24.2/35 earned "Dynasty" a fifth-place finish in the weekly ratings, halting a drift over several weeks that almost took the show right out of the Top 20 . . .
Wednesday, George Hamilton's tank of suntan oil blew up when he drove his car off the cliff with that awful Rita . . . but it looks like they both escaped. Meanwhile, where's Sensitive Steve's new wrestling friend, the lawyer? . . . And Finally
In Chicago, a woman who told police a television preacher angered her so much that she threw the TV set to the floor, causing it to explode, has been charged with involuntary manslaughter in the fire that followed . . .
A firefighter died in the Sunday blaze at the Mark Twain hotel . . .
And in San Francisco, the Coast Guard reports that a sailor aboard a fishing boat was electrocuted Wednesday when he picked up a wet television set that had been knocked off a table during a storm, 10 miles off the Golden Gate . . .