THE WORLD will have to wait for the fall to discover who shot J.R. Ewing. But starting this week, viewers have another way to get deep in the turbulent heart of Texas.

Tomorrow afternoon at 3, "Texas," a new soap opera set in Houston, premiers on NBC. "It'll be the 'Dallas' of daytime," brags NBC programming chief Brandon Tartikoff.

"If it sounds like a daytime version of 'Dallas'," says Daytime TV magazine, "Well, imitation is the sincerest form of flattery."

And there's more to come: NBC's afternoon round-up is only the beginning of what looks like a network trail drive into the Lone Star State: Big-spending Texas couple Bo and Asa Buchanan were created for ABC's "One Life to Live" last January; more and more Texan characters appear on prime-time programs; and ABC is preparing the series called "oil!" as a likely mid-season replacement for the fall.

Although "Texas" Executive Producer Paul Rauch denies the "Dallas" connection, his heart is deep in Dixie "Back in 1978 I worked with two writers, one from Houstron and the other from Shreveport on developing a daytime show called 'Reunion' about a girl who spent the Civil War in England and then returned home. It didn't get on the air, but last summer NBC asked if we would develop a contemporary show."

Many of the "Texas" characters are still undefined, but Rauch emphasizes that there will be "no archtypical villain" modeled after J.R. However, there will be "lust, sentiment and men and women bigger than life thrust into each other's lives," says Jason Bonderoff, editor of Daylight TV.

The new soap was created in one of the most elaborate spin-off plans in TV history.

Last May, fans of NBC's "Another World" (for which Rauch is also executive director) began to see new characters. Disillusioned by love, young Dennis Carrington moved from midwestern Bay City to Houston. His nasty mother, Iris, accompanied by her cranky maid Vivian, followed him. Iris loves to manipulate Dennis, her only son. And besides, she had become friendly with Reena Cooke, a former Texas belle married to Dr. Kevin Cooke. Reena got Kevin to move to Houston, and, of course, invited Iris. Last June, they jumped into a private jet, and since then half of "Another World" has transpired in Houston.

The best is yet to come: In her youth, Iris had a love affair with Alex Wheeler, now head of Houston-based World Oil (and more powerful than the entire Ewing family put together). Alex never married because for a quarter century he's nursed a love for Iris. The two meet again in Houston and flames flicker, but then Iris finds out about Vicki, with whom Alex has been having an affair for 15 years. In the last episode of "Another World," broadcast last Friday, Iris boarded a plan and flew away from Houston and Alex forever.

But Alex, like J.R. before him, likes to call the shots. Tomorrow, in the first "Texas" episode, he has Iris' plane called back, hustles her into a chauffered limousine, and holds her captive on his luxurious yacht.

Viewers fearing for the safety and virtue of Iris must stay tuned.

Despite its close clone-like similarity to super-hit "Dallas," the new soap faces a tough challenge. "Another World" has attempted two previous spinoffs -- "Somerset" and "Lovers & Friends" -- both of which failed. "Lovers and Friends" eventually became "For Richer, For Poorer," which disappeared several years ago, and was NBC's last attempt at innovation in the field.

Nonetheless, conditions may be favorable for a new daytime drama Nielsen figures show a slight increase in the audience for soaps, even though the percentage of women in the work force is also increasing. Experts believe the explanation lies in the new youth-oriented plots and sexuality injected into the shows, expecially by ABC. "They've been the hottest network for over 10 years," says a broadcast executive. "They do the most and they set the trends."

One reason for ABC's lead is that Procter & Gamble -- virtually the only soap company still in the soap-opera business -- owns only one of four ABC shows. "P&G ownership makes a big difference," says Bonderoff. "They keep a close watch on their shows, and they're very conservative." A P&G "memorandum on broadcast policies," quoted by media historian Erik Barnouw, in "The Sponsors" says: "There will be no material that may give offense to any commercial organization of any sort."

But NBC daytime programming chief Linda Line says that be a breakthrough program for P&G. They are sensitive to trends in public taste." Line claims to feel under little constraint. "I would do anything that would work as a good story," she says.

The stakes are high because soaps generate extraordinary profits. Internal NBC documents obtained by Variety recently reveal that for 11 months spanning 1979 and 1980, the 90-minute "Another World" (which finished third in its time-slot) took in $230,000 per broadcast in net revenues, cost $71,000 per episode, and consequently earned a profit of $159,000 per broadcast. By comparison, "The Tonight Show" earned net revenues of $190,000 and a $131,000 profit per broadcast.

With such figures, it's not suprising that NBC President Fred Silverman showed up at a cowboy-style barbecue at Rockefeller Center last week to celebrate the start of "Texas."

Silverman served as the CBS daytime programmer from 1962 to 1970. "He had a poor record," says Bonderoff. "He decided that soaps weren't viable and replaced them with game shows" But "Fred is very close to this area and feels very excited about "Texas'," says NBC's Line. "He and i decided together to put it on the air." NBC's flashy, provoctive promo ads for the new show have been running throughout the prime-time and daytime schedules. "It's the most ambitious campaign ever launched for the debut of a daytime program," says Line.

Ultimately, NBC need not worry about losing money. A recent Federal Communications Commission staff report -- based on examination of available network records spanning several decades -- concludes that " a daytime program series usually returns a profit from initial network exhibition, even if it is canceled after a brief run."

But NBC is after more than a profit. "We hope to set the standard for quality programming," says Line. "We want to say that characters can no longer sit around the coffee table and discuss their neighbors. We'll have more sophisticated plot devices and an upgraded production that will look like prime time."

Executive producer Rauch claims "Texas" "will revolutionize daytime television." He cites the extensive exterior shooting (soaps have been going outdoors more often since about 1978), the use of cinematic filters to achieve a softer look and brighter colors, and the full development of an identifiable city.

The other networks are sitting back in the saddle and waiting to see what happens before they, too, ride into Texas. "It's an interesting experiment. I'm glad to see it," says Jeanne Renick, CBS' east coast director for daytime programs. CBS, according to Renick, has no present plans for Texas-style spin-offs.

ABC's Jacqueline Smith says her network is working on "General Hospital," it will remain in the East. She is reserving judgement on "Texas": "All the scenery in the world won't help a show that doesn't have the necessary plot interest. Scenery is still scenery," she says.