They are as different as the famous photographs they make: one private, restrained, the other outgoing, eager to communicate.

But as art photographer Harry Callahan and portrait photographer Arnold Newman collapsed onto a bamboo sofa before their joint opening at Addison/Ripley Gallery last week, they agreed on one thing: They're both glad they got started in photography when they did--more than 40 years ago.

"Boy, that's for sure," said the 70-year-old Callahan, a bald, gee-whiz, American Gothic-type, whose honors include a 1976 retrospective at the Museum of Modern Art in New York. He reserves his eloquence for his art.

"Of course, Harry would have inevitably ended up on top any time, he's such a great artist," said Newman, five years younger than the man he calls "the great old master."

Many share Newman's view of Callahan as one of the greatest living American artists--in any medium. But Newman seemed less certain about his own hypothetical chances in the face of today's competition from thousands of good photographers, all garlanded with Nikons and expensive zoom lenses.

"I had studied art. It saved me," said Newman. His strong, handsomely composed portraits of Picasso, Stravinsky, Hopper and others in telling settings--most made on assignment for magazines such as Life, Look and Holiday--have made him one of the most admired and widely published chroniclers of the contemporary artistic visage.

"I had no art background. It would have ruined me," said Callahan, who was a 26-year-old accounting clerk at Chrysler Corp. when he joined a Detroit camera club for a hobby and had a life-transforming encounter with Ansel Adams.

"My belief is that you can't teach people to be creative. You can only educate," said Callahan, who subsequently made his living educating artists until he retired three years ago from the Rhode Island School of Design.

He now travels--often to his own exhibition openings abroad--with his wife, Eleanor, whom he immortalized in several early nude photographs, one of which hung nearby.

The real Eleanor sat patiently in the next room, chatting with Newman's wife, Augusta, and producing facts and figures that her husband had never bothered to store. Eleanor Callahan's long, lavish mane--which floats Ophelia-like beside her in a famous early photo in Lake Michigan--is now tucked neatly into a twist. But the features remain.

Newman says he did his best work on assignment, and early. "That portrait of Stravinsky--it was a reject from Harper's Bazaar. That Kuniyoshi was made when I first came to New York. My wife kids me that I'm still living off the sweat of a 20-year-old."

"I'm no good on assignments," said Callahan. "I've done a few. But I have to be free and on my own."

The poetic Callahan images that hang on the walls are the result of this intense solitude: a color-splashed autumn wood in Georgia; a vast, scale-defying stretch of beach on Cape Cod; a powerfully ominous street in Ireland, symbolizing two adjacent but distinctly different worlds.

Hands crossed over protruding waistlines, Callahan and Newman mused on the good and not-so-good old days--the camaraderie, the struggles. "I started out in '38 taking forty-nine cent portraits for sixteen dollars a week, and was glad to have the work," recalled Newman. "I remember when I could only afford to make eight or nine negatives at a sitting because of the cost of the film!"

"Yes, yes," said Callahan, nodding.

Newman now gets upward of $750 for making a print from one of his own negatives, and a vintage photograph of Alfred Stieglitz and Georgia O'Keeffe, taken in 1944, is for sale in this show for $2,400.

"I've done well," Newman allowed.

"I haven't," mumbled Callahan, but he would say no more on the subject. His color prints sell in the $1,000 range.

"Imagine being able to buy a Callahan for less than the price of a lousy painting. It's ridiculous," said Newman.

With survival no longer the issue, both photographers now have a new set of worries related to success: agents, contracts, estate taxes, copyrights. They share the same lawyer: Washington art specialist Ira Lowe, who suggested the Newman-Callahan show to dealers Chris Addison and Sylvia Ripley.

Money has also brought some luxuries. Newman has lab assistants who help him with the drudgery of printing, and Callahan--who never considered letting someone else handle his black-and-white prints--now says Kodak is his assistant.

"I only work in color now, so I just send off the roll of film to them, and they make the slides." He then selects slides and sends them to Germany where they are printed by the dye transfer process, which he calls "the most stable and best color process."

A question about changes in the market elicited simultaneous laughter. "There was no market before the 1970s," said Newman. "When I came along, there was only one curator and one museum collecting photography: Beaumont Newhall and the Museum of Modern Art. They were paying $10 or $15 for a print."

Newman recalled a Christmas show organized by the Museum of Modern Art in 1941 that included the work of nine master photographers, including Edward Weston, Berenice Abbott, Paul Strand, Charles Sheeler and newcomer Newman. "The prints were offered for sale in editions of 10 for $10 each. Not a single photograph was sold. Had someone bought them all, they'd be worth more than $100,000 today. The Sheelers alone are so rare that they'd sell for $12,000 to $25,000 each."

Newman, it appears, had the sense to buy a few. He also has several works of art bartered in the early days with artists he photographed, including two sketches for Mondrian's famous "Boogie Woogie," now on loan to the Museum of Modern Art.

Because a reporter had forgotten to bring a photographer to the interview, Newman offered his Minox, set at 12 feet, and began to arrange Callahan, leaving a space beside him for himself. A suggestion that they photograph each other was vetoed by Callahan: "I don't know how to do this stuff," he said. "I defer to Newman."

Placing a pen on the floor to mark the spot, Newman moved a reporter into place and put the camera in her hands with the instructions, "Push the button. Gently."

"I still always have to tell Eleanor not to move the camera," chuckled Callahan.

And they stood self-consciously before the lens--just like anyone else. CAPTION: Picture 1, Arnold Newman and Harry Callahan, whose joint show opened at Addison/Ripley gallery. By Jo Ann Lewis, assisted by arnold Newman; Picture 2, gia O'Keeffe & Alfred Stieglitz, New York City, 1944." Copyright (c) by Arnold Newman