What is the fatal attraction that keeps Sue Ellen coming back to J.R.?

That question is part of the intense marketing campaign to syndicate "Dallas," the smash hit produced for CBS by the Lorimar production company since 1978.

But despite its success -- one of the biggest TV audiences ever tuned in to the first episode in the 1980 fall season to find out who shot J. R. Ewing -- there is skepticism about the prospects for "Dallas" in syndication.

No one has rerun an hour-long serial -- a series with a continuing story line -- before, and the five-times-a-week schedule that is the norm for syndicated programming will require a steady and unusual commitment from prime-time viewers.

Thus, Lorimar has launched an aggressive public relations campaign to win viewers for reruns of "Dallas"; in addition to ads on radio, television and billboards, it is conducting a telephone contest titled "Dallas Confidential." Callers win a chance to ask J.R. a question, such as how to explain Sue Ellen's weakness for him.

The effort to syndicate "Dallas" and the improving prospects for "ad hoc" networks to compete with ABC, CBS and NBC are raising the Hollywood production community's hopes for new programming outlets. If the syndicators succeed with new forms for syndication such as "Dallas," it could signal the beginning of networks truly competitive with the three major networks. " 'Dallas' will build an audience just like it did in prime time, and it will be a springboard for a whole new form of television," predicted Pat Kenney, Lorimar's marketing vice president.

Program producers such as Lorimar are looking at a relatively new, potentially enormous market in first-run syndication, typified by gossip shows such as Paramount's "Entertainment Tonight," dance and game shows, and, for the first time, a new serial, "Rituals," coproduced by Metromedia Inc. and Telepictures.

The heavy competition for syndication dollars in a market that could reach $1 billion annually by the end of the decade stems in part from the fact that syndication revenue is what makes prime-time shows profitable. "The syndication area is very, very important to us," said Melvin Blumenthal, executive vice president for business affairs at MTM Enterprises Inc., the firm whose current first-run shows include "Hill Street Blues" and "St. Elsewhere."

"Without the possibility of a syndication marketplace, we couldn't produce these shows," Blumenthal said.

Producers here say there is no way that the first-run broadcast of a series episode covers the costs of producing a program, which can run as high as $1 million an episode for an hour-long adventure show. The so-called deficit, the gap between the license fees paid by the networks and the costs of producing the show, can be as high as $200,000 an episode, said Alan Horn, president of Embassy Communications, a production company co-owned by Norman Lear.

"The costs we are plowing into production are astronomical," said Harris Katleman, president of Twentieth Century Fox Television. "We can't produce shows at the prices we get from the networks."

These days, when a production company or studio decides to take on the production of a series, the decision more often than not depends on the show's ability to survive over three seasons, or long enough to complete 66 episodes, considered the minimum needed to make a show "syndicatable."

Earlier, so uncertain was the syndication market that producers routinely sold the rights to their shows to others for syndication distribution. Keeping those rights is now a cornerstone of the strategies of both the smaller independent producers and the major studios.

Moreover, syndication has emerged as such a vital ingredient of television success that some executives hesitate to go forward with the production of a series unless they are convinced of its syndication potential. At a time when the networks are quicker than ever to pull the plug on a struggling series, those production decisions are becoming more and more dependent on judgments about syndication prospects.

"In the old days you automatically said 'yes' when you thought you could get a commitment from the network," said Steven Roberts, the president of Twentieth Century Fox Telecommunications. "We turned down a show with a network commitment from a top creative team because the deficit and schedule positioning wasn't worth the risk. The whole risk-reward thing has turned around."

The burgeoning strength of so-called independent television stations has opened up a host of new markets for syndicated programming. Close to 100 new over-the-air independent stations have gotten off the ground since 1979. Moreover, distribution costs are rapidly shrinking as satellites replace telephone lines.

"The aftermarket has grown beyond our most optimistic expectations," Horn said. As an example of Hollywood's hopes, LBS Communications, a branch of Lexington broadcasting, is preparing to launch a two-hour package of daytime syndicated programming next year to challenge the historic dominance of the networks during that period.

The growing markets help explain the intensity of the two-year-old political debate over the Federal Communications Commission's efforts to ease the financial interest and syndication rules. The potential of these markets also explains why Hollywood fought so hard against an initial decision by the FCC to overturn long-standing rules barring the networks from the syndication business.

The commission had voted to let the networks into the syndication business gradually with full syndication rights available in 1990. But the commission's decision mobilized Hollywood lobbying and campaign funds, bringing both Congress and the White House into the dispute. The FCC is backing away from its ruling, and the matter is likely to fade for the time being.

While the networks have a host of profitable enterprises, officials at relatively small production companies such as MTM insist they couldn't operate in an environment in which the networks not only distributed the initial run of prime-time programming, but also could syndicate the shows in the "aftermarket."

As the new markets have grown, so too have a variety of payment schemes to encourage sales. For example, advertising time is bartered for programming, and a variety of other mechanisms are available to market the new programming. "The competition for 'shelf space' is greater now than it's ever been," Roberts said.

For all the activity, there are also risks. "Rituals," the $15 million, five-day-a-week syndicated serial that recently was launched in many major markets, has fared poorly in the ratings. And for all the hype about "Dallas," no station in Washington or Baltimore has picked it up.