THE MOMENT OF TRUTH is at hand for Hollywood’s newest fixation — the $ 100 million movie. Following “Waterworld,” thousands of stories have been churned out speculating about the impact of these megapics on audiences and studios alike. Well, it’s showtime. Most studio chiefs argue that by the time the dust settles, the $ 100 million picture will have achieved the same respectability as the notion of paying $ 15 million to a movie star. Superstar vehicles, these seers suggest, have proven to be Hollywood’s safest bet — witness Tom Cruise in “Jerry Maguire” or Jim Carrey in “Liar Liar.” Special effects are the new superstars of the ’90s, it is argued, and despite the cost, the new genre of effects-laden megapics will prove to be sound investments. Well, maybe. At this point in time, things look dicey. With 20th Century Fox’s “Volcano” still struggling to push past the $ 40 million mark almost a month after its release, some supporters of megapics are growing antsy.AND THE STRUGGLES over “Titanic” are making them even more so. Fox and Paramount are still at each other’s throats about a release date. Fox, not surprisingly, wants an August release, while Paramount would settle for November. Any further delays would open up the possibility that this three-hour mother of all megapics will cross the $ 200 million mark in negative cost — rumors about even higher numbers are being firmly shot down by responsible sources. Meanwhile, the town also is quietly gossiping about the budget of “Batman and Robin.” While Warner Bros. is skilled at staying below the radar, sources suggest this project, too, soared past $ 100 million in full flight. All this would not only raise the bar for megapics, it would nuke it. Even before the economics of the $ 100 million picture have been assessed, we’re faced with the $ 200 million monster. Does this make any sense? Anyone who saw the premiere of Steven Spielberg’s “The Lost World” last week would have to say, “OK, I get it.” This isn’t only a superbly created movie, it’s a potential industry, replete with theme-park rides, toys and myriad other ancillary benefits. And apparently its cost didn’t even climb close to $ 100 million. Where are the merchandising benefits in “Titanic,” one might ask? Will there be a theme-park ride where passengers drown? Or perhaps a toy that gurgles from the bottom of the bathtub? IT’S AGAINST THIS BACKGROUND that a succession of megapics will now open, including “Batman and Robin,” “Men in Black,” “Starship Troopers,” “Face/Off,” “Alien Resurrection” and “Speed 2: Cruise Control.” Make no mistake about it, there are big bucks on the table. “It’s like a casino where all the bettors have become delusional,” says one veteran talent agent. Again, will these wagers prove sound? It’s hard to assess the record to date without getting bogged down in definitions. Arguably, the first megapic was “Cleopatra,” which in today’s dollars cost the equivalent of $ 300 million. It was a disaster. The first “modern” $ 100 million movie was probably “Terminator II” — it was a hit, but still helped sink Carolco, which produced it. Along the way came a bunch of marginal megamovies — only the accountants really know whether they were winners or losers. Universal has consistently claimed that it will make a few bucks on “Waterworld,” which, despite all the denials at the time, ended up costing more than $ 160 million. “Eraser” was another marginal megapic from Warner Bros. On the other hand, there was nothing marginal about “Cutthroat Island.” This $ 100 million swashbuckler was a total turkey, though it was the independent distributors around the world who felt the lash, not a Hollywood studio. There was also nothing marginal about “Twister,” “Independence Day” and “Batman Forever.” They were not just winners, they were windfalls that forever changed the economics of the movie industry. Because of their success, the multinational corporations that own Hollywood decreed that the future belonged to megapics — that $ 100 million movies represented the soundest and safest investment for their global distribution platforms. AND WHILE THAT REMAINS the prevailing wisdom as the curtain rises on the summer of ’97, there are already signs of mini-defections. Bill Mechanic, the thoughtful chairman and CEO of Fox Filmed Entertainment, has come to the conclusion that “it’s ludicrous to believe that an event picture has to cost $ 100 million.” While Fox this year has placed its bets not only on “Titanic,” but also on “Speed 2,” which is rumored to have come in at around $ 125 million, Mechanic insists that his studio’s next round of megapics will consist of shrewdly planned, character-driven projects that will be made on more contained budgets. Two examples are the remake of “Doctor Dolittle,” starring Eddie Murphy, and a movie based on “The X-Files.” George Lucas also plans to bring in his “Star Wars” prequel at well under $ 100 million, sources note. Even as these cautionary voices are being heard, however, yet another round of $ 100 million megapics are being mobilized around town. Whether they’ll actually go before the cameras or not may depend on the results of the summer. Indeed, by summer’s end, the Hollywood megapic may either be enshrined forever or sink to the bottom like the well, let’s not get into that again.