Getting viewers to "tune in next week" is hard enough, but at the end of a TV season, networks and producers have an even tougher job: convincing viewers they should tune in again next fall.

Result: the proliferation of the cliffhanger, a device that strands various characters on brinks and leaves plot lines dangling tantalizingly at the end of a show's season.

It's that time of year again. Tonight at 8:30 on Channel 9, the season finale of "Dallas" will spend 90 minutes enticing viewers to rush back to their TV sets in the fall. It's another in a long string of efforts to duplicate the record number of viewers who tuned in to the fateful 1980 episode of "Dallas" that posed the famous question, "Who shot J.R.?"

The creator of that granddaddy of prime-time cliffhangers, Lorimar president Lee Rich, says from Hollywood that the reason for the widespread use of such teasers is simple: "You've got to get the audience back, and that's the way you do it. You do it every week, and you do it at the end of the season."

And lately the phenomenon hasn't been limited to prime-time soaps. Comedies, capers and dramas are endeavoring to give their viewers exasperating summers.

"Hill Street Blues" fans will be left wondering about Frank Furillo's renewed battle with alcoholism, and "St. Elsewhere" fans are still asking themselves how the normally stable Dr. Westphall could have left the hospital.

Audiences are not the only ones held in suspense by cliffhangers. Many actors have to sweat it out over the summer as well. If an actor wants to leave a show or the producers are looking for new blood, nothing keeps their options open as well as a calamity, particularly if no bodies are found.

If an entire cast is getting testy, one can follow "Falcon Crest's" lead and put them all in a plane hurtling toward certain destruction. This immensely improves the producers' positions at the negotiating table.

Among this year's expanded crop of cliffhanging shows, and the questions they leave dancing in viewers' heads:

"Cheers" (aired May 9) -- Sam Malone was on a plane to Italy hoping to halt the marriage of Frasier and Diane, who has once again misjudged her beloved jock and, believing that he's ignored her plea for interference, has convinced Frasier to marry her immediately. Will Sam stop Diane from marrying Frasier? Will Sam marry Diane? Will Carla, Cliff and Norm die of disgust?

"Remington Steele" (May 14) -- Laura Holt was last seen sitting forlornly on the end of Remington Steele's bed after realizing that her latest request for a trial separation had driven the enigmatic movie buff out of her life. And where is the debonair sleuth? Well, London's a safe bet since next season's first two episodes will take place there. But will Steele return to a life of crime? Will Laura find him and convince him to return to the agency? Will they ever stop bickering long enough to consummate their relationship?

"Dynasty" (May 15) -- The season went out with more than one bang. Fallon, still unaware of her own identity, left L.A. and headed for "the mountains" while Sammy Jo plopped a wig on Krystle's "double" to make her look just like Krystle. Meanwhile, after Amanda and Prince Michael said their vows, ABC unleashed what it had billed as "the most explosive conclusion in television history." A gang of terrorists dressed in fashion fatigues crashed the ceremony, leveling guests with machine-gun fire. As the ever-perceptive Krystle shouted "They're trying to kill us!," the entire cast of characters hit the deck. Will any of the wedding guests die? Will Krystle survive to face Sammy Jo's revenge? Will Jeff survive to join the cast of his new series, "Dynasty II -- The Colbys"?

"Dallas" (tonight) -- Just as star-crossed lovers Bobby and Pam are finally getting back together, Bobby will be run down by a car driven by the mysterious woman seen shredding Jenna's picture last week. (Although the red fingernails seem to implicate Katherine Wentworth, careful viewers who noticed the woman's gray hair may prefer to bet their money on Amanda Ewing). J.R. will convince Miss Ellie that Sue Ellen is "a tramp, a drunk and an unfit mother" and that loser Barnes will give Jamie grounds for an annulment. Will Jamie agree to the annulment? Will Dusty keep Sue Ellen out of the "drunk tank"? Will Patrick Duffy realize that $40,000 an episode isn't such a bad deal after all? (The answer to the last one is no -- he is leaving the series.)

"Knots Landing" (Thursday) -- Dr. Ackerman's suicide will send Mack and Karen on a frantic search for clues to the whereabouts of Val's babies. Abby will try to save her marriage and what's left of her soul by taking Val to the babies. But before everyone converges on the twins' home, their adoptive father will run away with them. Frustrated fans should take note: Lorimar president Rich says the search will be resolved quickly in the fall. Will Val get her babies back? Will Abby get what's coming to her? Will Val find something new to be traumatized about?

"Falcon Crest" (May 24) -- Melissa will confess to framing Lance for the attempted murder of his mother. Cole will tell Melissa that her cousin is pregnant with his child. Richard and Lance will be devastated by Lorraine's death. Connie will do her best to break up Maggie and Chase. Will Cassandra and Damon succeed in destroying Falcon Crest? Will Melissa be sent to jail? Will Cole make an honest woman out of Robin? Will Joseph ever have a chance to live in a normal home?