Ka-boom! No, that was not a one-gun salute to Captain Airwaves. That was the sound of the "Today" show coming back to earth yesterday . . .

Nielsen figures for the week ending April 5 revealed that despite its Holy Week stay in Rome -- and on-air promotions for the show featuring Pope John Paul II -- the NBC early-morning program could do no better than tie ABC's "Good Morning America" in the ratings . . . although it did manage to beat "GMA" by a single share point for the week . . .

Overnights in the big cities had suggested that "Today" was going to be a big winner last week but the national averages gave "Today" a 5.5 Nielsen rating and a 23 percent audience share, compared with "GMA's" 5.5/22 and "CBS Morning News' " 3.6/15 . . .

Although "Today" was unable to outdistance its ABC rival, it did manage to finish first (or tied for first) for the third week in a row, and that hadn't happened since the month of April 1981 . . . when the NBC show actually won five weeks in a row . . .

And the 5.5 rating was also its highest since the week ending Jan. 29, 1982 . . .

On Monday, the Committee for a Sane Nuclear Policy (SANE) will unveil a "multi-media advertising campaign designed to raise the issue of human rights atrocities committed by the contras in Nicaragua" at a Capitol Hill press conference . . .

As part of the campaign, a 30-second TV ad, produced by Bill Zimmerman of Santa Monica, Calif., will be aired in selected markets around the country . . .

WJLA here has accepted the ad, but a SANE spokesman yesterday acknowledged that both WRC and WDVM had rejected it as "too controversial" . . .

Channel 7 cleared the ad only after receiving documentation supplied by SANE backing up the allegations in the ad, which pictures a Nicaraguan family, three members of whom were allegedly murdered by the contras . . .

The TV ad and two different radio spots will be aired in key congressional districts around the country, according to SANE. One radio spot has been accepted by WTOP in this market . . .

The campaign, which also includes print ads, is aimed at Congress, which is expected to vote soon on aid to the contras . . .

Today's unconfirmed rumor from the Coast: that Barbara Bel Geddes will return to "Dallas" as Miss Ellie next season. The story has appeared in the Hollywood trade publications, but yesterday spokesmen for both CBS and Lorimar Productions refused to confirm or deny . . .

Bel Geddes retired from the show last season after heart surgery and was replaced in her role as the Ewing family matriarch by Donna Reed . . .

One actress who is not returning to TV is Loretta Young. She was due to start work Monday on a pilot for a new Aaron Spelling ABC series, "Dark Mansions," but her manager announced yesterday she had withdrawn from her role because of "creative differences" . . .

Spelling, who produces "Dynasty," among many other ABC series, said, "It is true that we had creative differences over the way her character was developing. She is a great star and a great friend and I hope she remains both" . . .

Norman Brokaw, Young's manager, said he was authorized only to say there were creative differences. "She is a professional and she had to do what was right for her professionally," he added . . . Also in the News

For the last couple of seasons, CBS and NBC have been sitting on the sidelines on Wednesday nights waving feebly as ABC's high-powered trio of "The Fall Guy," "Dynasty" and "Hotel" raced by with most of the nation's viewers in tow . . .

While neither has been able to dent ABC's lead from 9 to 11 p.m. this year, NBC has finally established its share of the 8 p.m. action with its successful "Highway to Heaven" . . .

And now CBS, after no success with sitcoms in that hour earlier this year, has come up with "Double Dare," starring Billy Dee Williams, and Wednesday night's debut indicates CBS, too, may have a winner . . .

In Nielsen's 10 major markets, "Double Dare" beat the competition with a 15.1 rating and a 24 share, compared with "Fall Guy's" 13.8/22 and "Highway's" 13.3/21 . . .

On Channel 9 here, "Double Dare" was even more popular, with a 16.8/28, compared with an 11.5/19 for "Highway" on Channel 4 and an 11.2/19 for "Fall Guy" on Channel 7 . . .

After seven weeks, the U.S. Football League on ABC is averaging a 5.5 Nielsen rating . . .

That's down 21 percent from its 7.0 rating after seven weeks in 1984, although the 5.5 matches its season-long average last year . . .

The crew on "CBS Morning News" Tuesday morning presented coanchor Bill Kurtis with a basketball they'd all signed, saluting his "team spirit" . . .

The gesture touched Kurtis, who has been getting a lot of ink in the Chicago and New York papers lately speculating that he was (1) dying to return to Chicago and a rumored $2-million-a-year offer to be a local anchor, (2) unhappy with coanchor Phyllis George and (3) causing, because of all the conjectures, unhappiness on the "CBS Morning News" set . . .

In the April 15 issue of New York magazine, "Intelligencer" pointed out that one Chicago story about Kurtis was written by Gary Deeb, whose agent, Donald Ephraim, is also Kurtis' agent . . . but Ephraim denied to New York that Deeb got the stories from him . . .

Before Kurtis came to "CBS Morning News" as coanchor with Diane Sawyer in 1982, he had been a successful evening anchor for WBBM, the CBS-owned station in Chicago . . .

The New York story quotes Ephraim as saying that "it's not clear that CBS has made the best use of Bill's journalistic skills." Regarding the $2 million offer, Ephraim told New York, "I'm not going to deny that. Everybody in Chicago has approached me about hiring Bill" . . .

One source at CBS News, who claims to know what management is thinking, insists that "Bill is hurting morale on the show. It's an open secret that he didn't get along with Diane who has moved on to "60 Minutes" and now with all this talk about Phyllis, it's as if he can't work with a woman and that could hurt him, even when it's not true" . . .

This source said CBS News management would like Kurtis to tell his agent to pipe down. "I think the feeling upstairs is that Bill's contract isn't up until next March and he should be spending more time working on the morning show" . . .

We ran those comments past Kurtis yesterday and this is what he told us: "I've asked Don if he'd fed any of those stories and he said no, but I must say his comments have been upsetting. He's overtalked. Maybe he's been more aggressive than would have suited me . . .

"You have to understand about the Chicago press," Kurtis added. "They generate things out of thin air" . . .

As to the comments about his attitude on "Morning News," Kurtis repeated what he had said at a recent Washington press conference. "Phyllis and I get along just fine. She's easy to work with. And Diane and I got along fine and we still do. We're good friends. There's always going to be sort of a general struggle between news and entertainment on a show like we have and maybe that affects relationships once in a while, but only temporarily . . .

"With all those stories, I'll admit it's been difficult. But I want to keep my job. I'm not shipping out. There's really never been any substance to any of the rumors" . . .

Kurtis sounded a little weary as he talked about the gossip but brightened considerably when the conversation got around to his recent "A Gift of Life" documentary on CBS dealing with organ transplants . . .

"You know, we've gotten all kinds of wonderful mail about the program," he said, "a lot of them expressing thanks for giving people hope. And there's been an increase of donors, too, as a result of the program. I'm very proud of that" . . .

We asked Kurtis if Phyllis George had signed his "team spirit" basketball . . .

"Oh, yes," he said. "And she wrote, 'We love you,' too" . . .