THEY CALL themselves Orion, after the great hunter constellation of stars. For the last year, they have been shaping an entity which some observers say is the first important new movie company to appear in decades.

Five men run Orion: Arthur Krim and Robert Benjamin, co-chairmen, Eric Pleskow, president, and Mike Medavory and William Bernstein, vice presidents. They were the top executives at United Artist until they resigned, en masse, in January of last year, in a move that shocked the film industry.

Their activities in the year since their bold departure have been equally dramatic. They raised $100 million in credit from seven banks with their fe ulative experience and expertise as collateral, signed stars such as John Travolta, Jane Fonda, Diane Keaton, Peter Sellers and Peter Frampton to make pictures for them, and now have, in various stages of development, three dozen projects and a minimum of 10 -- and possibly as many as 15 -- movies to be released in 1979.

Orion's first movie to reach the screen is due shortly before Easter in New York and Los Angeles (by summer, nationally). It's "A Little Romance," directed by George Roy Hill ("The Sting"), co-starring Laurence Olivier and Sally Kellerman and two newcomers, Thelonious Bernard and Diane Lane. It's described by Orion as "a contemporary love story featuring two 13-year-olds." Youth seems to be prominent on the '79 Orion lineup of films. The next production is "Mouse Packs," a story of suburban kids going wild, due in May.

Among the Orion films due in the fall are "Heart Beat," starring Nick Nolte, Sissy Spacek and John Heard. It's based on a romantic triangle about the Beat Generation heroes of the '50s, Neal and Carolyn Cassady and Jack Kerouac. Another promising-sounding project, slated to film this February, is "Simin," written and directed by the witty Marshall Brickman, who shared the Oscar for writing "Annie Hall" with Woody Allen, and starring Alan Arkin. Peter Sellers will star in "Fu Manchu" and "Chandu the Magician" sometime next year.

Orion has signed two-picture contracts with Jon Voight, James Caan, directors Lindsay Anderson and Blake Edwards and producer Jon Peters (thereby, indirectly, with Barbra Streisand, who is supposed to star in and direct a movie for Orion), as well as with Frampton, Sellers, Travolta, Keaton and Fonda. Nick Nolte has a four-picture deal.

The story of the formation of Orion is significant for what it reveals about the dynamics of the movie business today.

In 1967, Krim and Benjamin sold United Artists to a button-down, to a button-down, insurance-dominated conglomerate, Transamerica, in order to have a diversified economic cushion for the bad years. (In 1970, a terrible year, UA lost $85 million.)

But a year ago, when Krim, Benjamin and their chief production executives abandoned their company, United Artists was the industry's biggest moneymaker and winner of more than its fair share of Academy Awards. Why did they leave?

Not in a dispute over creative control. There was no interference from Transamerica in decisions regarding which movies to make, the executives have admitted. The issue was money. Krim and Benjamin wanted a piece of the action for their three younger associates. They were told to be satisfied with salaries with fixed ceilings and limited stock options. At 20th Century-Fox and Columbia Pictures Industries, which have resisted conglomerate takeovers, the top officers reward themselves handsomely with profit-sharing in their company's blockbuster hits.

When Krim was prevented by Transamerica from spinning off a company to give Pleskow, Medavoy and Bernstein a share in the profits their decisons were making possible, the scene was set for the walkout. The usual remors percolated in the trade papers. It was assumed that the UA team would break up and become, individually, freelance producers or that they would jointly replace their counterparts at one or another of the less successful movie companies.

Instead, they confounded everyone by forming Orion. The company is owned by the five. Therefore, they share in the profits, if any, from their managerial skills.

There is no disputing the fact that Orion is operating on a grander scale than any movie company not considered a "major." How unique the new organization is, and how well it can achieve its goals, remains to be seen.

The unusual niche that Orion occupies at the moment is what makes defining its status and predicting its future as a trend-setter so problematic. Because it gets its own credit from a consortium of banks, Orion is not dependent on the whims of the major movied distriubutors to finance its productions.

But to get its movies from the producers who make them to the theaters that show them, Orion needed the services of a farflung movie distribution company -- which is what the Orion executives had, automatically, at United Artists. So Orion made a deal with Warner Bros. to be housed with them at their Burbank studio facilties, and to use the older company as their distribution organization.

The nature of the Orion-Warner Bros. relationship has still to be defined, refined and tested. At this point, it is unclear how what has been described by Eric Pleskow as "a body (Warner's distribution) with two heads (Warner's and Orion)" will function.

Pleskow said in a recent conversation that he considers Orion a distributor of its own movies. "We set the release plan, the terms, the dates, choose the theaters, design the ad campaign," said Pleskow. "The Warner Bros. offices will monitor each movie's performance for us." By which he means that rank and file Warner Bros. staff will work under the control of Orion supervisory personnel. What happens when Warner Bros. -- which pays the staff workers -- has a movie opening about the same time as an Orion movie, and time and loyalties must be divided? The answers won't be forthcoming for a while.

Clearly, Orion has a special appeal to some filmmakers. "Orion is the first place you go to offer your project in Hollywood," director Phillip Kaufman said in a recent interview. His "Invasion of the Body Snatchers" was commissioned by Medavoy while he was still with United Artists. Kaufman's "The Wanderers," an early '60s movie about adolescents growing up in the Bronx, is currently being edited for August release by Orion.

"They give you a quick decision -- no stalling, like most places," Kaufman continued. "And then they don't stand over your shoulder and look at the dailies. Once the deal is made, they trust you and essentially let you make your own movie.

"They're nice guys. It's a very personal company. I can call Arthur Krim anytime, if I really have a problem. I can have lunch with him, or any of them. They are five guys who are always available. It's not like working for Universal, where Lew Wasserman's a man of mystery."

The men of Orion established solid reputations for the personal touch. And it is the triumph of the personal over the corporate system of interchangeable managers and intransigent treatment of talent that Orion represents at its best.

Some admirers of Orion have forecast that within a couple of years United Artists will be an empty shell, as contracts with filmmakers like Woody Allen, who originally signed with Krim and company, expire and the talent follows the crowd to Orion.

But the new management at United Artists has taken steps to assure new sources of supply. A three-year contract with Lorimar Productions for 13 pictures has been signed and Lorimar has five movies ready for 1979. Lorimar's biggest experience has been as a producer of TV shows.

And the situation is very fluid. Not all the talent that worked with the team when they were at United Artists has climbed aboard the Orion bandwagon. Director Hal Ashby, who made "Coming Home" for the five executives at United Artists, is signed to a multiple picture deal with Lorimar. Ashby's first finished film is "The Hamster of Happiness," a comedy with Robert Blake and Barbara Harris. Ashby is now preparing "Being There," a comedy with Peter Sellers adopted by Jerzy Kosinsky from his novel.

Orion makes a point of describing itself as a movie distributor -- even though it plans to use a borrowed staff to perform its distribution functions. The reason is that otherwise, its classification might be confused with that of a producer for the major movie studios. The Orion team thinks of itself as a new movie company -- a full service organization. Other major producers, like Ray Stark, will be making pictures for Orion, Pleskow took pains to emphasize.

Producers abound in moviedom. Metro-Goldwyn-Mayer, for example, is now just a producer of films -- four or so a year -- distributed by United Artists for a fee.

Almost anybody with investment capital, a hot property, a star or a director can be a producer in today's movie market. The ultimate power rests, however, with the movie company -- the middleman, broker, financier -- that has the distribution network to get the movie to your local theater.

Orion may be the newest and brightest movie company in Hollywood since RKO in the '30s. Or it may be just a rich-kid investor. Stay tuned for further developments.