At the urging of his bosses, Dan Rather substantially altered his delivery on "The CBS Evening News" for the first week of August. He was low-key. He talked slowly and quietly. He was a Valium.

On Monday, the new Dan Rather was ditched and the old Dan Rather returned. "I listened. I tried to soak up the advice and counsel of more than a few people around here about how to improve my performance," Rather said yesterday. "I tried it and it didn't work."

CBS News will have to find some other way of raising the ratings of a broadcast that for years was proudly in first place and now, often as not, finishes the week a humbling third. Changing Rather into Danny Do-Right was prompted by a belief that his at-attention manner of delivering the news is too "intense," and that "NBC Nightly News with Tom Brokaw" is often No. 1 because viewers find Brokaw soothing and relaxing.

"I kept hearing that we should be laid-back, homogenized, yuppie-ized because that's the fashion of the '80s," says Rather. "I don't know that to be true. I'm not sure I even know what it means. I don't know how to do that well and I am not sure I want to.

"I'm a worker, and I'm a learner," Rather says. "I'm trying to learn this so-called '80s style, but I don't really believe in it."

For CBS News, the fall from supremacy by its flagship broadcast is the latest in a continuing, almost self-parodistic series of organizational calamities. Asked if he has been agonizing over the ratings and whether he blames himself, Rather says, "Probably yes on both counts. I see it as accountability. Increasingly what happens in society is nobody steps forward to say, 'I'm accountable.' Being managing editor of this broadcast means I should be responsible for the broadcast. Not totally -- it's a collective endeavor -- but largely."

Rather does not claim, as some in TV news occasionally do, that the ratings mean nothing to him. "The scoreboard lights up every Tuesday," Rather says, referring to the day the previous week's ratings come out. "And when we look up on Tuesday now, the news has not been very good." Last week, the "Evening News" was third again, a sliver behind "ABC World News Tonight." NBC was first, its 17th week in the top slot.

Reportedly, CBS News President Howard Stringer and "Evening News" Executive Producer Tom Bettag were among those urging Rather to be cooler, softer and more dispassionate on the air. One CBS News insider says Rather took the advice to a somnambulistic extreme to make the advisers look silly. Rather denies this.

That Rather is too "intense" has become an industry cliche', and it doesn't explain why his newscast was No. 1 for 214 straight weeks, since he has been intense all along. Since the ratings are so mercurial, and since the "Evening News" ratings are affected by many factors irrelevant to the quality of the program, Rather is asked why he doesn't just ignore them and plunge on. "Most of the time I can," he says. "Most of the time I have. This is not one of those times."

Asked how long he could countenance being in third place, Rather says, "For a long time. How long can anybody else countenance it, I don't know." Competitiveness in TV news may be higher now than it's ever been, and all three network evening newscasts are probably in better competitive shape than they've ever been. The kind of easy lead CBS once enjoyed over puny rivals (and that NBC's "Huntley-Brinkley Report" had in its long heyday) is widely believed to be extinct for any network.

Ratings for the "Evening News" are adversely affected by, among other things, the lousy job CBS Entertainment is doing in prime time (where record low ratings have been set this summer); the poor showing of local newscasts which precede Rather at CBS-owned stations in some major markets; and the overall ratings juggernaut that NBC has become throughout the day and night.

But however many mitigating factors there are, the perception has taken hold that the once-indomitable "CBS Evening News" is a broadcast in trouble, deep trouble. Rather says summer is a good time to test new ideas and to assess the weak points in the program. He certainly doesn't cotton to the idea that he is a weak point himself.

Rumors persist of plans afoot to team Rather with a coanchor, perhaps Diane Sawyer, but executives and spokesmen regularly shoot them down. It would be precipitous, insiders believe, to make any such changes before the 1988 elections, partly because elections tend to bring out the best in Rather and the top-ranked CBS News correspondents.

Will there be any "radical changes" evident in the Rather newscast come September, once the summer experiments are over? "Whatever else you may have read to the contrary, Dan Rather is not a radical," Rather says. "We're adjusting and looking and trying to push ourselves to improvement."

Rather says published rumors that he is thinking seriously about retiring from the brutal hurly-burly are preposterous, and that despite all the turmoil, he has hardly reached the fed-up point yet.

"No. No way," Rather says. "Absolutely not. I'm not the fed-up type. I'm the get-up-and-do-something type." It is unlikely anyone who has worked with Rather for more than 15 minutes would disagree with that assessment.

Some CBS News competitors say Rather is much more the victim of CBS woes than the cause. "They were the New York Yankees, the House of {Edward R.} Murrow," says one network executive. "They've lost that. It's been tarnished." The news division faltered under the gimmick-minded Van Gordon Sauter, former president, detractors say, and it has been pummeled by budget cuts mandated by CBS chief executive Laurence Tisch.

About anything bad that could happen to a news division has happened at CBS. But Timothy Russert, hard-driving executive vice president of NBC News, says the division has made its own serious blunders. One was relinquishing the morning news time now dominated by NBC's "Today" show and ABC's "Good Morning America." CBS News threw in the towel and gave up the time to the entertainment division, which inflicted the dismally inane "Morning Program," a ratings bust from the word go.

"From 7:30 to 9 a.m., they've abandoned news coverage," Russert says. "You can't do that. You've got to be there." An alert, aggressive "Today" show helped NBC "develop a reputation for being a pace-setter, for being ahead of the news in the morning," Russert says, and the "Nightly News" benefited from that.

NBC News also proved its prowess during crisis coverage, Russert thinks. Polls show NBC was able to reverse completely public attitudes about which network to consult when a crisis hits.

CBS News may have been so busy fighting its own crises that it suffered in its ability to cover those of the real world.

Russert mentions another reason for NBC's growth in the ratings. He calls it "the comfort factor." He says viewers are comfortable with Bryant Gumbel and Jane Pauley on the "Today" show and with Brokaw on "Nightly News." The question is, how much comfort should an anchor provide? Rather is commonly acknowledged to be the most authoritative anchor on the air. Peter Jennings of ABC News is considered "effete" by many, and Brokaw still suffers from a callow boyishness.

But if Rather's passion and zeal for the news, and for his job, are scaring viewers away, what does that say about viewers? "Max Headroom," the supposedly computer-generated anchorthing and talk-show host starring on ABC and on Cinemax, might be the future of TV news after all.

Rather, despite his insistence that he wants to hang tough and slug it out, also says he can conceive of not being the anchor of "The CBS Evening News." Isn't a national anchor's job like the president's, in that everything after is anticlimax? "I don't think so," Rather says. "I've had so many good jobs that I know I can be happy doing a lot of different things." Then he waxes wistful about having spotted a black bear during a recent fishing trip in upstate New York, and of being so impressed that he took a step backward and fell into the drink.

"It's been 25 years since I've seen a bear in the wild," marvels Rather. "I saw a wolf, too." He sounds so much more excited about this than about contemplating the next harebrained scheme to boost the ratings of "The CBS Evening News."