As Hollywood cheerfully toasted the advent of the New Year, I felt the urge to hoist a little sign that advised: Warning, the year ahead may be hazardous to your health.You don’t have to be an oracle to recognize the sweeping changes overtaking the entertainment industry — changes that are triggering layoffs, spreading widespread angst and revolutionizing how we think and work. And it’s not just about techie stuff. As John Brodie writes this week, Hollywood is feeling the impact of a major generational shift. New filmmakers, new stars, new ideas and a new generation of decision-makers arepushing their way to center stage. None of this should come as a surprise. A quick glance at Hollywood history reveals that seismic shifts seem to occur at 25-year intervals. If that pattern holds true to form, then brace yourself — it’s tremor time again. I realize that Hollywood tends to be obsessed with the present and to ignore the past, but bear with me a moment while we do a little kaleidoscopic year-surfing. Twenty-five years ago, Hollywood was on the brink of a renaissance but was too depressed to see it coming. Five of the seven major motion picture companies were in the red, and just about all were on the block. A whole new band of filmmakers with names like Spielberg, Lucas, Coppola and Scorsese were knocking on the door, trying to tell us that they could reverse the downward spiral, but the studios were ready to bail because they’d lost half their audience in the years since World War II. That’s how bottom-feeders like Kirk Kerkorian were let into the party. By contrast, exactly 50 years ago, in 1945, the studios were basking in postwar euphoria as well as record profits. An adoring audience embraced virtually anything Hollywood could create. Only very alert seers were noticing that, amid the awesome affluence, the audience was starting to shun downtown movie palaces and to flock to the suburbs, where an intriguing new medium called television was starting to grab their attention. Hollywood was too smug to notice that it was dancing on the edge. It was 75 years ago when a tight little clutch of former exhibitors managed to tie up the infant film business in a neat little oligopoly — one that laughed off the protests of a band of dissident artists named Charlie Chaplin, D.W. Griffith, Mary Pickford and Douglas Fairbanks. In forming United Artists, a sort of DreamWorks Part I, these stars and filmmakers reminded their “owners” that movies were dependent not just on money but on talent, pledging to protect the public from business interests that would “force upon them machine-made entertainment.” The reaction was one of outrage: If stars demanded “clout,” next thing you know they’d even want a piece of the action! Every 25 years, it seems, Hollywood finds itself confronted by fearsome portents of change, which it chooses to ignore. Hollywood’s charm is also a fatal weakness: It is so obsessively narcissistic that it is incapable of pausing, taking a breath and acknowledging that change is at hand, that events may soon be spinning out of control. Thus in 1970, when Hollywood was hitting bottom, there was no voice that heralded, “Wait a minute, guys, don’t abandon ship. Think about video, imagine the impact of a blockbuster, dream about the overseas market, hand over the keys to a new generation.” Is another changing of the guard at hand today? Certainly several portents would hint that such is the case. Veteran filmmakers have had a tough year — witness Pollack, Donner and Friedkin — and studios are turning more to newcomers for economic as well as artistic reasons. Emerging stars like Brad Pitt and Sandra Bullock are shoving aside the Newman-Beatty-Nicholson generation. The quality of television programming as well as the range of choice on TV is beginning to overshadow the movie business. Cyberspace poses an ever greater lure to the high-end audience. “There is something wrong with the mainstream structure of the film business, ” John Calley of United Artists told Brodie. Twenty-five years ago, when Calley was the production chief at Warners, the studios were pinned to the wall and “had to throw out the formulaic stuff and start making decisions that were braver.” At Warners, along came “Deliverance” and “A Clockwork Orange,” among others, to lead the way. The key question, however, is whether today’s bureaucratized studios are capable of the “braver” decisions, or are sealed off from innovation by their hierarchies and cost structures. The similarities among current movies would lend support to the latter thesis. Yet the scent of change hangs in the air. At least two of the major studios are expected to undergo executive makeovers during the coming year. MGM/UA is positioned for another change of ownership. Corporate megamergers will further alter the Hollywood landscape. The 25-year milestone may once again take its toll. Yes, it will be an interesting, if dicey, New Year.