WASHINGTON — Washington. --There is no entry on ''hair'' in the index to Lou Cannon's fat new book on the Reagan presidency. Nor in Ronald Reagan's own autobiography. So we must rely on Kitty Kelley. The index of her ''Nancy Reagan: The Unauthorized Biography'' contains four citations on Mr. Reagan's hair.
And under ''Reagan, Nancy Davis, hairdressers of,'' citations go on for three lines. The key reference is on page 292. ''Whenever he visited the White House to color the First Lady's hair, Julius also dyed the President's gray roots, which he had been doing secretly since 1968.''
This revelation might strike most people as less interesting than Ms. Kelley's allegation that Nancy was canoodling with Jerry Lewis on the desk in the Oval Office. (Have I got that right?) But many will find it a good deal more plausible. A small matter, perhaps. But you can read the saga of Mr. Reagan's hair as a metaphor for the 1980s, when deceit by public officials reached new levels of respectability. Mr. Reagan set a new standard of brazen duplicity of which George Bush and future presidents are the beneficiaries.
Mr. Reagan is legendary for his ability to insist with seeming sincerity that black is white (or, in this case, that white is black). The hair question is worth cherishing for its starkness. The usual muddling devices are not available.
He cannot claim he didn't know they were dying his hair. He cannot claim he can't remember. He cannot blame the Congress for dying his hair against his will. He can't say it's a matter of national security. And it's not one of those complicated questions the nation learned to give Ronald Reagan a pass on.
The press approach to the hair question went through phaseslike the phases in its general approach to Mr. Reagan's truthfulness. Phase one, before he became president, was a fairly energetic skepticism. Mr. Reagan was forced repeatedly to deny that he colored his hair.
Mr. Reagan claimed that during his governorship, Sacramento reporters stole some his clippings from the barbershop floor and found no artifice. This became a treasured part of the Ronald Reagan Anecdote Collection, repeated by Nancy as recently as 1989, embroidered with the assertion the hair had been sent for laboratory tests. It surfaced just last year in a ''Dear Abby'' column -- moved to the Reagan presidency and enhanced by having the reporter work for ''one of those gossipy newspapers (sold primarily in supermarkets).''
Phase two came in the early White House years, as reporters wearied of trying to expose every falsehood. Most reporters assumed he dyed his hair, but despaired ever proving it or making anyone care.
At this point a second theme started to emerge: Mr. Reagan is starting to turn gray. In May 1982 the New York Times reported that Senate Majority Leader Howard Baker had ''noticed some gray in Mr. Reagan's hair.'' The next month, the Times itself declared that Mr. Reagan's new, puffier style seemed to ''do more to show off his traces of gray.'' In November 1982 the London Guardian observed that the miracle hair, ''sleek brown and shiny when he took office, is notably grayer now.'' And the Washington Post confirmed the next month: ''His once jet-black hair is now streaked with gray.''
Phase three was during and after the triumphal 1984 re-election. Even the cynical Washington press corps came to believe in the Reagan magic. Maybe a man who can carry 49 states really can approach his eighties with a full head of naturally brown hair. Meanwhile the London Financial Times observed, in January 1985, ''His still luxuriant brown hair may be beginning to show traces of gray.''
In phase four, the failures and disappointments of Mr. Reagan's second term reignited doubts, but the myth basically survived. A vTC conservative activist, enraged at the president's half-hearted support for Supreme Court nominee Robert Bork, said, ''Maybe Reagan does dye his hair.''
The Financial Times observed in August 1987: ''The loss opublic trust is at last turning Ronald Reagan's hair gray.'' In September 1988 the Washington Post detected ''a few gray [hairs] poking through.'' And a December 1988 Post valedictory noted, ''There are streaks of gray in the mane of black hair, so envied by his rivals.''
Then came phase five. Shortly after he left office, Mr. Reagan's head was shaved for brain surgery, and briefly, as it grew back, his hair was completely gray. At a speech in December 1989, ''Mostly the audience stared at Reagan, whose gray hair was the main subject of conversation.'' How to explain it?
No fear. Soon enough, Mr. Reagan's hair was once again just beginning to turn gray. A Washington Post review of his televised Poindexter trial testimony: ''His still wavy hair has swirls of gray.'' The Post, February 1991: ''Except for the streaks of gray in his black hair, Mr. Reagan seems to have aged little since he left the White House.''
Maybe he doesn't dye his hair. A decade of shock discoveries that his hair is at last turning gray suggests a scarier possibility: it's been gray all along! But Mr. Reagan's had us so hypnotized we can't even see it.
TRB writes commentaries for The New Republic.