In the baroque seven-tiered lobby of the Brown Palace Hotel, a photographer is taking a picture of a photographer taking a picture of a photographer taking a picture -- and nobody finds this phenomenon the slightest bit unusual.

It's the kind of thing you have to expect, after all, when professional photographers get together. And this week a star-studded team of 200-plus photojournalists from 27 countries has gotten together on assignment for what is arguably the biggest photo opportunity in U.S. history: 24 hours in the life of America.

On Friday, May 2, the "shooters" -- as the photographers like to call one another -- will fan out from sea to shining sea to snap some 200,000 frames of the land and people of the U.S.A. A team of editors will then cull the best 300 or so, and the result -- due in the bookstores next fall -- will be published as a colorful, high-gloss coffeetable book to be titled "A Day in the Life of America."

To construct this pointillistic portrait of the nation, the photographers will poke their lenses inside refrigerators and under boardwalks. They will shoot atop Mount McKinley and at the bottom of Grand Canyon. They will focus on a missile silo in Minot, a Maharishi meditation in Keokuk, a rasslin' match in Tulsa, a Klan bash in Georgia and a dope bust in Miami.

Canadian photographer Doug Kirkland will shoot the first frame of the 24-hour extravaganza at the first gleam of dawn off Maine. He'll then race cross-continent to catch the last glimmer of twilight as the sun drops west of Hawaii.

Meanwhile, special guest photographer Larry Speakes will be shooting pictures aboard Air Force One as it carries President Reagan toward Tokyo. This fits the ground rules, the project's editors argue, because the president's plane is legally considered U.S. territory, wherever it may be.

The three shooters assigned to Washington will be inside the Supreme Court with Warren Burger, outside the White House with Mitch Snyder and among tourists as they photograph the Capitol. Other Washington-area assignments include oyster boats on the Chesapeake Bay, the Marine Terminal in Baltimore, the Blue Ridge Parkway, the Navy base at Norfolk, the Virginia horse country and the mines and factories of West Virginia.

The $5 million photo op is the most ambitious endeavor yet by the hyperenergetic young photographers and editors who have so far produced stunning pictorial books on a "A Day in the Life" of Australia (1981), Hawaii (1983), Canada (1984) and Japan (1985).

The patriarch of the project is 36-year-old Rick Smolan, a globe-trotting photographer who dreamed up the general idea six years ago during an eight-month assignment photographing the Australian outback for National Geographic. Along with editor David Cohen, the organizational brains of the mission, and Spencer Reiss, a Newsweek reporter who is serving as managing editor, Smolan has spent most of a year making plans for America's day on film.

They recruited a blue-ribbon list of photojournalists that includes nine Pulitzer Prize winners and such luminaries as Carl Mydans, a member of the original Life magazine photo team, and Frank Johnston, three-time winner of the White House News Photographers' Photographer of the Year award.

A smattering of amateurs will also take part. Former Senate majority leader Howard Baker will be shooting the Kentucky horse country, and Colorado Gov. Richard Lamm will be poking a camera around Denver.

Although text plays a small role in the "Day in the Life" books, the editors are looking for a writer who can help capture the essence of America. Editor Reiss said he hopes to persuade Joel Garreau, author of "The Nine Nations of North America," to accept the assignment.

In a media-soaked nation, of course, a big media project like this becomes a media event in its own right. And so the shooters will be accompanied on their assignments by camera crews from all three television networks and a PBS documentary team. Sometime Friday evening, an NBC-TV cameraman will be shooting Russian photographer Vladimir Sichov as he shoots the NBC News cameras shooting Tom Brokaw delivering the nightly news.

Smolan, a master of commercial barter, has worked out an intricate network of corporate tie-ins with companies willing to help out in return for a plug in the book and the right to use the pictures in promotions.

United Air Lines, for example, is giving all the shooters free passage to their assignments. Hertz rental car will handle transport on the ground -- and will also give $3,000 to the photographer who comes back with the best picture that just happens to have a Hertz Rent-A-Car in it ("no rear shots, no muddy cars," the company has decreed).

Kodak will process all 6,500 rolls of film -- but only if the shooters use Kodak film. In return for setting up headquarters here in Denver, the project got free hotel rooms and a nearly endless string of parties from civic boosters.

The photographers are to be paid a flat fee of $500, but that's just the beginning. Each will also receive a barrel of corporate goodies ranging from Nikon hats, Waldenbooks tote bags and Merrill-Lynch briefcases to Sony compact disk players and $3,000 Macintosh computers from Apple, which is both a major sponsor of the project and one of the specified assignments on the long list the shooters will shoot.

For many, the project is also a chance to shoot pictures they have long dreamed of. Many of the American photographers asked to go back to their childhood hometowns for this assignment. French and Polish shooters, in contrast, fought hard to get out to the wild West and take pictures of cowboys.

During the meetings and parties this weekend, though, many participants said the best part of the job was just being a participant -- being admitted to the stellar crew of professionals who are picked for a job like this.

The gathering had the feel of a slightly bohemian class reunion. Hour after hour, photojournalists who had last seen one another in a bar in Managua -- or on last year's "Day in the Life" excursion to Japan -- shook hands and started back in on conversations interrupted months or years before.

What do shooters do when they mass together? They carouse some and complain some -- about colorblind editors or overpriced cameras. But mainly they shoot: picture after picture of anything that happens to fall before the lens.

One of the prime photo subjects for all the shooters here was the grandfather of the "Day in the Life" team, Carl Mydans, the sprightly septuagenarian from Time-Life who is legendary in the trade for his world-famous photo of Gen. Douglas MacArthur, corncob pipe in teeth, wading ashore at Luzon in 1945. When Mydans was introduced at the group's initial meeting here, the entire assemblage burst into a loud, affectionate ovation.

Evoking Mydans' achievements, editor John Durniak then delivered a pep talk to the assembled shooters. He started slowly, but built up to a socko finish: "Go out there and shoot the hell out of the country."

With a lusty roar, the "Day in the Life" shooters agreed to do just that.