For 70 years, nobody, it seemed, could make a serious dent in the door of Hollywood’s heavily fortified ”closet.” Despite the town’s private tendencies toward tolerance, the public rules about homosexuality were clear: If you were an actor who happened to be gay or lesbian, you were expected to do some of your best make-believe off screen, mimicking heterosexuality at least well enough to keep nosy columnists at bay — or, failing that, well enough to keep straight people from minding the truth.

But over the last two decades, and especially in the past five years, more and more ”friends of Dorothy,” to use an old coded phrase, have been pounding away at that showbiz closet door like the Tin Man chopping through the gates of the Wicked Witch’s castle. In 1982, thwack! — an ex-boyfriend sued Liberace for palimony, thereby unleashing a flood of blunt revelations that had been kept dammed up by the flamboyant entertainer’s successful 1959 libel suit against a British newspaper columnist who implied he was homosexual. By 1985, whack! — Rock Hudson, the biggest on-screen hetero stud of ’50s Hollywood, had died of complications from AIDS, exposing once and for all the most elaborately ”bearded” existence ever engineered by duplicitous publicists. And last year, kablooey! — off came the hinges forever with one little ”yep” from Ellen DeGeneres in TIME magazine, backed up by a confessional interview with Anne Heche on Oprah.

You’ll find vivid analyses of such over-the-rainbow-flag milestones in David Ehrenstein’s Open Secret: Gay Hollywood 1928-1998. You’ll also find sizable, if scattershot, smatterings of old-Hollywood sociology (like where the homosexual watering holes were in the ’30s and ’40s, and why straights like Bogart blithely frequented them), as well as a remarkable, oral-history-style sampling of extended remarks from a host of current industry folk, ranging from big fish (David Geffen) to directors and producers (Gus Van Sant, Clive Barker, Laurence Mark) to in-the-trenches personnel like Steven Dornbusch, a blue-collar grip who dishes on just how graphically gross crew members can get about gay sex.

The problem is, you won’t find these fresh, worthy elements within an especially sensible — or even scrutable — chronology. Despite his orderly sounding title, Ehrenstein, a frequent contributor to the Los Angeles Times and Daily Variety as well as the author of a highly intellectual Martin Scorsese career salute, is one of the least linear historians you’re ever likely to encounter. In the book’s first half, he ping-pongs maddeningly back and forth through the decades, never lighting in one place for long. When he does pause, it’s usually to let one of his witnesses literally take over his book, chattering on for three or four pages at a clip like Owl in a Winnie-the-Pooh tome. Delicious as some of these monologues are — I would hate to miss former Warner marketing director Chris Pula free-associating his way through the studio’s most dreadful recent movies and declaring ”Being a cynical queen…has made me a good marketer,” or film critic Kevin Thomas reminiscing at great length about director George Cukor — they range all over the map from personal confessionals to gay-rights advocacy to sheer unfiltered chatter. In the wake of at least a dozen such undigested broadsides throughout the book, it’s difficult for Ehrenstein to get back into gear, and he grinds horribly trying to slap ludicrous transitions over the holes.

Of course, he’s taken on a massive, difficult subject, and that’s part of what defeats him. How can one survey Hollywood gay history without broad swatches of national gay history? How much should be put in or left out? It’s usually when Ehrenstein narrows the spotlight that he’s most successful, as in a terrific chapter about the preponderance of gay sitcom writers in recent years. In such segments, he brings a welcome, steady compass to barely charted territory. The rest of the time, his information and his sources are engaging, but you’ll wish he’d presented it a little, well, straighter. B-