DAVID STEINBERG, GUESTING ON “The Tonight Show” several years ago, told the following joke:An elderly Jewish woman is at the beach baby-sitting her grandson, who is playing near the shore. Suddenly, a huge wave washes over the boy and drags him out to sea. “God,” the woman says, looking skyward, “I’ve never asked anything of you before, and I’ve lived a good life. Please, return my grandson to me, and I swear I’ll never ask anything of you again.” With that, a large wave washed up again, this time depositing the boy back on the shore, coughing, but unharmed. The woman looked skyward again. “He had a hat …” ASKING MORE OF CBS after its historic third-to-first turnaround last season may seem a bit unfair, sort of like that elderly woman. Still, in light of the pounding NBC has taken over the past several months, it’s helpful to see that even a first-place network can have its share of problems. CBS’ performance this season remains solid, well ahead of second-place ABC in terms of household ratings and a reasonably competitive second among adults 18- 49. On a night-by-night basis, however, one can see the soft spots on its schedule, betraying how difficult it is to maintain the No. 1 chair, as NBC did for six consecutive years before the start of its current slide. A November sweeps loss to ABC underscored CBS’ tenuous grasp on the top position at a time when viewers seem more responsive to stunting than series. And though off to a good start in the current sweeps, the Eye web will need the six-hour miniseries “Queen” to perform to forestall a similar indignity in February. CBS made a savvy long-term move a few weeks ago when it secured the services of Angela Lansbury for two more seasons of “Murder, She Wrote,” assuring the web’s Sunday franchise along with “60 Minutes” and the Sunday movie. The two movie slots, in fact, have really emerged as the unsung heroes of CBS’ hold on first place, along with “Rescue 911.” Monday has been the other key part of the CBS success story, though that franchise has shown some vulnerability. “Murphy Brown” is in its fifth season and, after the Dan Quayle flap, on a downward cycle creatively. Diminishing ratings could be on the horizon. Fortunately, “Northern Exposure” continues to come on strong, along with “Murder” far outranking any other dramas on network TV. OF MORE CONCERN, the two new comedies that have fleshed out the night, “Hearts Afire” and “Love & War,” haven’t demonstrated the potential to be much more than time-period hits–i.e., shows reliant on tent-pole scheduling for their audience. Moreover, one has to wonder whether Linda Bloodworth-Thomason–with four more series commitments to fulfill–is spreading herself a bit thin, whatwith three series on the air in addition to helping out the Clinton administration. “Rescue 911″ (along with “Murphy,” the best legacies of former entertainment chief Kim LeMasters) has grown this year against declining competition, and with clever scheduling Tuesday seems relatively secure. Those three nights represent the nucleus of CBS’ week-to-week power, and while the network has made progress elsewhere, for the most part the Wednesday-through-Saturday schedule has proven at best a mixed bag. The Friday lineup hasn’t turned out the way CBS might have hoped but has improved matters, and the web will likely renew “Bob” and “Picket Fences”–one more new series than survived the 1991-92 campaign. Maintaining that Friday comedy franchise will be no small trick, however, with more “Designing Women” cast changes in the works (Annie Potts has expressed a desire to do her designing elsewhere) and “Golden Palace” not performing as the network might have hoped. The Wednesday lineup also relied on a migrated NBC series, “In the Heat of the Night,” currently in its final season, leaving the 8-10 p.m. block up for grabs next year leading into “48 Hours.” The demise of the last major prime time soap, “Knots Landing,” may also be a significant blow to Thursday–since the viewer loyalty those shows command, even with declining shares, won’t be easily equaled. CBS’ best news of 1993 remains “Dr. Quinn, Medicine Woman,” the 8 p.m. Saturday prescription for which all three webs were searching. The challenge will be to find a compatible lead-out–no small task, since “Dr. Quinn’s” success remains largely a mystery. As for the web’s other big coup–the signing of David Letterman– CBS may discover that wanting Letterman is more fun than having him. While deserving of the overused designation “comic genius,” Letterman requires a good deal of care and feeding, and the process of launching his show–under microscopic scrutiny–should offer its own unique array of headaches. It’s hard to believe that only two years ago, CBS had to gripe about the modifying line “mired in third place” following it around, the same way “Medicine Woman” trails “Dr. Quinn.” Mired no more, and understandably cocky about its resurrection, CBS will claim its second consecutive household ratings crown when the prime time Nielsen term expires in mid-April. In the current broadcast environment, however, uneasy lies the crown of network television. If you doubt it, just ask NBC. STATUE AT LIBERTY: Well, the Academy of Television Arts & Sciences has gotten the Emmy into another fine mess, and no matter which side you believe in the latest rhubarb, it’s time for a little statesmanship on everyone’s part. Yes, the Academy probably should have gone with a rotating four-network broadcast wheel, if only to prevent the sort of acrimony generated by its exclusive arrangement with ABC. That said, feuding over the show does little to benefit any of the excluded networks, the Emmys, or for that matter the viewer, who couldn’t care less which channel carries the show. The Emmys can still serve as an industry showcase, and rumored punitive measures by the other webs won’t benefit anyone. If NBC, CBS and Fox are truly miffed about ABC’s exclusive deal, they can retaliate by aggressively programming against the Emmycast. And if ABC fulfills its vow to “return the stature to the statue,” it won’t make any difference.