Ever since the dawn of the space age, whenever anybody wanted to throw a satellite into orbit, they had to contract with NASA to get a rocket to do the job.

But NASA is finally getting some competition. The European Space Agency, using its Ariane booster, has begun competing with NASA for space shots, already winning away a few Intelsat launches from the U.S. space shuttle. And now Martin Marietta Corp., the Bethesda aerospace giant, is entering the game with its Titan III booster, long one of NASA's favorite rockets.

In a battle that experts say could mean a lot to the future of private space efforts, Martin Marietta, in partnership with Federal Express Corp., is vying with NASA and the Ariane for a contract to launch three huge, new communications satellites for Intelsat, the international satellite consortium.

Due to be awarded in September for launches in the middle of the decade, the initial contract could be parlayed into a chance to launch several more satellites for Intelsat, the biggest nongovernment user of rocket boosters. "We launch a lot of satellites," quipped Intelsat spokesman Gavin Trevitt after ticking off the consortium's crowded launch schedule for the next few years.

A victory in the battle for the Intelsat contract could be a big first step in Martin Marietta's plans to sell Titans as private launch vehicles. But a loss of the contract could mean the end of production for the venerable Titan, which NASA is phasing out in favor of the shuttle after 25 years as a space workhorse. Martin Marietta hopes to continue production by selling Titans to private users.

Martin Marietta's private space effort is a joint venture with Federal Express, which bought out the original partner, Spacetran, in May and renamed the operation Fedex Space Transportation Co. Fedex puts together the deals and Martin Marietta builds the rockets, which are to be launched from Cape Canaveral or Vandenberg Air Force Base in California.

Although the stakes are high -- the initial contract will be for more than $100 million -- Martin Marietta makes enough off of missiles like the MX and the Pershing II to more than cover the Titan's disappearance. But the company's Denver Aerospace Division is competing hard for a chance to make the commercial rocket business a big part of Martin Marietta's future.

"We could use that as the anchor tenant or the bell cow that could start us off," Gareth Flora, program manager for the commercial Titan, says of the Intelsat contract. "We're working on how to win that and parlay that into a commercial Titan business."

The contract Flora is so interested in is to launch the latest series of Intelsat satellites, the Intelsat VI, a two-ton, $100 million communications satellite with about three times the capacity of current communications satellites. Intelsat has ordered five of the satellites from Hughes Aircraft and has an option for 11 more. The first two launches, beginning in 1986, have been assigned to the shuttle, but the other three in the first group, plus any of the satellites on option, are up for grabs.

Intelsat has been alternating between Ariane and the space shuttle for its current series of Intelsat V spacecraft, and had expected to choose between them for the Intelsat VI.But the availability of the powerful Titan is a new factor.

And Intelsat, frankly, is pretty happy with that. "We're sort of sitting back and basking a little in the fact that we have some competition that we can go to," Trevitt says.

When it gets right down to cost, it would appear that the choice is pretty simple. NASA officials say they can launch Intelsat VI aboard the space shuttle for $52 million a flight. The Titan and the Ariane are more expensive -- about $75 million a shot for the Titan, somewhat less for Ariane. They cost more because, unlike the shuttle, the Titan and Ariane are one-time-only vehicles that cannot be reused.

But Intelsat isn't looking strictly at cost. It's also interested in reliability and availability of its chosen launch vehicle.

Under those rules, the Titan and Ariane have some advantages, principally because they can guarantee a launch date more readily than the shuttle. With the shuttle's crowded launch schedule, a technical mishap could delay a launch by months. But Ariane has had its problems, too, failing twice in six launches, although experts expect it ultimately to be very reliable.

So Martin Marietta's best selling point, to cop a line from partner Federal Express, might be that the Titan would be a good choice if the satellite absolutely, postively, has to get there. "We think seriously that the Titan is still the right answer for Intelsat," Flora says.

John Logsdon, a space policy expert on leave from George Washington University, agrees. "They would argue that they could offer reliable launch dates and system reliability," he says. But that advantage is fading, he adds. "As the shuttle becomes more and more a routine operation, that premise is a bit undercut," Logsdon says.

Both Titan and Ariane may have another edge. Intelsat likes to vary its choice of launch vehicles, both for political reasons and to ensure that it will have some sort of a backup if something goes wrong with one launch system. Since the shuttle has already been assigned two of the Intelsat VI launches, Intelsat may use one of the other boosters for the succeeding flights.

Even NASA's shuttle marketers concede that point. "We expect that they'll give them out to Ariane or to the Titan, but we'll keep trying, and we expect to get our share of them," says Michael Goeser, a customer-service manager ("As far as descriptive titles, that's really what we do," he explains) at NASA. "We marketed hard for the first two and we'll market hard for the remainder," he says.

But Martin Marietta and Federal Express are also marketing hard. Worried that the shuttle's price advantage might still prove to be the biggest factor in Intelsat's decision, Fedex is spending the summer, as negotiations with Intelsat proceed, shaving its price.

"My view is that if [Titan or Ariane] is not close enough to the shuttle to make it attractive to Intelsat as an alternative, they'll go to the shuttle," Flora says. He believes that a cost differential of 20 to 40 percent more than the shuttle would make the Titan -- or the Ariane, for that matter -- fully competitive in Intelsat's eyes because of the reliability and scheduling advantages.

With a Titan carrying a price tag, unlaunched, of up to $60 million and launching services adding another $15 million or so, how can Fedex cut the price? "That's called a management challenge," Flora says with a laugh, adding that the company is considering strategies to reduce the price by spreading development costs over a longer period or taking advantage of some research and development tax breaks.

Should it miss out on the Intelsat project, Martin Marietta might not get another chance to sell the Titan commercially. There are no other equivalent contracts on the horizon that would justify keeping the Denver Titan plant operating. The other major satellite projects in the planning stage are either too small to use Titan's huge amount of thrust or nowhere near ready to launch. For that reason, Intelsat VI is of paramount importance.

"We've got to have some pretty good assurance that there are some customers out there," Flora says. "They've been the first people who are extremely serious and are ready to write contracts.

"They're not messing around," he adds, a touch of urgency in his voice. "They're picking launch vehicles."