It is Thursday of Three Mile Island week, and the art directors of People and Look are in awkward situations.

Before the nuclear mishap, People had scheduled a "China Syndrome" Michael Douglas/Jane Fonda cover, but now the image of their two smiling faces seems out of place. Art director Bob Essman spends hours looking through transparencies, ultimately switching to one showing a toothy, half-smiling Fonda and a smirking Douglas.

On Friday, as the nuclear threat mounts, Essman will add a small image of the plant's cooling towers and a headline that was not possible two days earlier: "A Disaster Movie Comes True."

Across town, Look has a similar problem with it Jane Fonda cover, also scheduled before the Harrisburg problem. The biweekly is due on newsstands one week after the Academy Awards, with a printing schedule that won't allow a last-minute makeover. So design director Regis Pagniez ships two covers to the engravers.

One declares, "Jane Fonda: The Winner"; the other, "Jane Fonda: The Real Winner." The Fonda profile is tucked into the magazine's black-and-white news section, next to a terse, comprehensive article on the Three Mile Island implications by Evans and Novak.

This kind of eleventh-hour guess-work is only one of the vexing challenges in the iffy and frenetic world of a news magazine art director-"the awkward position," as former Parisian Pagniez puts it, "of balancing words and pictures and still selling magazines."

"The work is not just layout," he says. "We make a magazine out of nothing."

The process begins in the evanescent realm of ideas, which the editors pump out weekly in story conferences. Once the concepts are agreed on, a writer and photographer are assigned to each story.

At Life, Look and People-photo-magazines by definition-words tend to get the short end of the stick.

"Basically," says People photo editor Mary Dunn, "all three of us are fitting words around pictures."

Loo k's Pagniez agrees: "I always ask the writer first, ''Do you write a lot of words or a little words?' And if he says 'a lot,' I try to get him to make less so there is more room for the pictures to breathe."

And on top of it all, there is the work of editors, those hard-headed folks who often manage to offend both parties: by killing phrases while simultaneously knocking a picture out of a layout to get more space.

"When that happens," says Dunn, "I just go running into the layout room and fight to the death for my photographers."

Not all of them are worth defending, but a photographer whose style is compatible with the subject is valuable enough to champion.

"You can't really tell someone how to shoot something." Dunn says. "you don't have time. I must go through 6,000 pictures a week. What you wind up doing is picking a central picture and then fanning out. You can get to feel pretty sure about an image, and really want to fight for it."

She's going through hundreds of prints of works by an unknown Italian painter for an upcoming story.

"No one knows who he is," says Dunn. "So you want to see him in this home-here-with his dog on the table and-here-in the local cafe."

Dunn then passes to Essman an edited selection of the photos.

"I call my work undesigning," he says. "I just want to let the pictures live on the page. Sometimes I'll ask for the whole take, but these things run into thousands of images."

"As far as art directors are concerned," says Bob Ciano, art director of the new monthly Life, "the worst advance in the history of photography was the motorized camera."

The pace of news deadlines compounds the problem for art directors and photo editors. A National Geographic story may take a ful year of work. Art directors at slick mags such as Playboy and Hustler can order classy die-cuts or airbrush art six months in advance. But those options aren't available in the uncertain arena of trends, earthquakes and assassinations.

News magazines have inherited the odd, subjective discipline of art direction that was defined in the early days of Vogue and Bazaar, when layout men tucked words around sumptuous fashion shots by some of the world's greatest photographers: Beatton, Munkaschi, Stieglitz, Steichen and later, Penn and Avedon.

"You could say that Alexi Brodvitch, the design director at Harper's Bazaar, was the real father of this field," says Ciano. "He used to run a design workshop in the evenings at Avedon's studio, which was where I learned pretty much everything I know."

While the fashion magazines were struggling through the Depression, Henry Luce was adapting their large, protography-heavy format into the new-oriented style of Life-a magazine that was to effectively define photojournalism.

"I didn't really like the way the old Life looked," says Ciano. "But you're talking about reworking the Old Testament."

"Life developed a format," says John Durniak, former Time photo editor and until recently managing editor of Look. "Luce showed the world that photographs are evidence, facts that can knock a point home graphically. Somehow the size of Life then, and now the size of Life and Look, allow you to tell stories with photographs as we couldn't do at Time.

"Still, there's been a tremendous change in the way photos are used in Time and Newsweek: color, much snappier, much more immediate. Think of the impact of the Jonestown stories without those photos. Is wasn't like TV footage; you could linger over the images."

With the changes have come sharply contrasting views of photo esthetics.

"We would not have been as negative about the Vietnam war if it had appeared in black and white," says People's Essman. "In a magazine, color can tend to have an unreal quality to it, and color photographs made the war horrifying in an unreal way."

Look's photo editor, Elaine Laffont, thinks differently.

"Black and white is more dramatic," she says. "Pink and blue doesn't have the same effect. We're numb to color from watching television. Black and white is more cutting." That edge can be crucial in the intensely competitive world of news magazines.

"With Look's biweekly schedule, I have to find a theme that's not so topical," Laffont says. "This is the only way we can compete. So in Iran, for instance, I told the photographer I wanted photographs of revenge ."

"Look is very direct and lively," Life photo editor John Leongard says of the competition. "They're good with black and white. We haven't done many black-and-white photo essays. We should be doing a lot more, and we're looking."

But whatever their differing formats and theories of design, there are some irreducible similarities. Essman sums them up:

"What I've got to do is keep people visually interested all the way through the magazine. I'm not terribly interested in arty pictures-a nice photograph sitting on a page with white space around it and you're wondering what the hell it's there for I'm interested in pictures that tell a story so that people can understand the thing easily."

One of the most successful vehicles for pictorial storytelling is Look magazine. But the man responsible for the much praised look of shrugs off compliments. Regis Pagniez is slouched on a couch in his ver uncluttered, sun-filled office.

"I rest here and receive persons," he says.I don't want to work in this area. It is important to rest sometimes."

Pagniez walks into an expansive room where layouts are spread aound the wall making up an entire issue of the magazine. Additional stories are pinned below the three rows of material that will be "in the book."

"You see," he says, "a magazine must be like life: Sometimes you are busy and sometimes you rest. I look at this wall and I can play with the balance of the magazine. I can change the rhythm, like music. I look for a little head, a big head, a real rhythm.

"I pick the 10 better pictures and I make them different sizes with the stat machine and then I try to see how they will look in different combinations. Sometimes a not-so-good picture can make a story easy to understand."

He's going through pictures of Patty Hearst's wedding.

"It's hard to make a good layout of this because we have not a lot of pictures. But this (a picture of Hearst with husband Bernie Shaw in his police uniform, she wearing his cap) is a wonderful picture because you remember she was in jail for two years. So you use it big. Or this (a picture of Elvis Presley being kissed by an unidentified fan in the '50s). No one has seen this, so you spread it out over two pages. You must not be afraid to be bold."

"Unfortunately," he says, "we are almost always stuck with using people on the cover. No real events are being photographed right."

"Photography," concurs Ciano, "has become terribly introspective. There are no strong pictures. So everybody is using headshots."

He pauses for a moment and thinks. "Maybe it's because there haven't been any wars. They really helped photojournalism." CAPTION: Picture 1,2 and 3, Look's cover for a fast-changing week, designed by Regis Pagniez, upper right, below, from left, Robert Essman of People and Life's Bob Ciano; photos by Donal F. Holway for The Washington Post