JAMES MILLS FIGURES illegal drug dealers around the world earn a half-trillion dollars a year, and he adds, for those who need imagery to grasp that figure, "A half-trillion dollars would weigh more than the entire population of Washington, D.C."

Industrialists on that scale, needless to say, have lots of well-placed friends. "Over a period of six years," he writes, "I became convinced of the participation in the drug traffic of high officials in at least 33 countries." He includes the United States, of course, but -- except for the CIA, whose "still-fresh footprints" he claims to have seen in a number of major narcotics camps -- he is unfortunately vague about who or how.

Efforts to stop drugs at the border are phony; it can only be done at the source. Using this standard, he finds all presidents guilty by reason of apathy, except Nixon, who was "the only president ever to make the battle a serious foreign policy issue." Ronald Reagan's War on Drugs, which Mills considers "a joke," can be measured by the $50.2 million the United States spent to control drugs around the world in 1984 -- "less than the value of a single load of cocaine." If our leaders weren't less concerned with cocaine overdoses and "marijuana-fogged seventh graders" than they are with maintaining diplomatic relations with criminal governments, says Mills, they would twist the arms off Peru, whose coca amounts to half of all the cocaine consumed in the United States, and Panama, "the world's cocaine banker," and Mexico and Colombia, whose profits from drugs "probably amount to 75 percent of their total export earnings."

Instead, the United States goes along with the charade of Latin American cooperation. "A Colombia Navy patrol boat, provided at a cost of $2 million by the United States, operating in the most smuggler-infested waters in the world, had in two years searched only fifteen vessels. It seized one kilo of cocaine, some marijuana residue, and a small amount of American currency. Of two hundred arrests made by a Colombian Customs boat (also a gift of the United States), only four defendants had been convicted and all of them subsequently 'escaped.' "

If President Reagan is still in the mood to retaliate against terrorists, he might want to consider bombing Bogota. Mills lists two full pages of anti-American terrorists attacks by Colombian drug dealers seeking revenge for our lack of hospitality.

But let's not get too serious. Only a minor part of The Underground Empire is addressed to the author's outrage. Most of it is about spirited narcs-and-dealers chases.

ONE NIGHT in 1979 at a Washington party Mills heard some guests talking about "Centac," and when he asked what it was, the answers were "politely evaded or ignored." And yet the next day he was taken, "without warning or explanation," to a hideaway suite "in one of Washington's most notorious wino-junkie neighborhoods," to meet Dennis Dayle, head of Centac, an elite corps of 50 agents in the Drug Enforcement Agency, who spent the next four hours answering every question Mills could think to ask.

Hey! What remarkable luck! Why was he chosen for that flood of candor when, he says, up to that time "no more than a handful of men in the world understood completely what Centac was and what it did"? We don't get an answer. Nor do we learn why, a few weeks later, the DEA decided to let him have access to some of its secret files and tag along, tape recorder humming, on some of Centac's operations.

My guess is that DEA wanted some classy publicity to use at budget time and it knew Mills could handle both nonfiction (The Prosecutor) and fiction (Report to the Commissioner), and had a good sense of humor and a sometimes Saturday-matinee style that would go nicely with the DEA's usual blend of fact and fiction.

If that was the motive, Mills produced too late. Centac was killed when the Reagan Administration reshuffled the drug enforcement bureaucracy.

The Underground Empire can serve as Centac's eulogy and sarcophagus. It is sometimes floridly windy enough for the one ("Like a solitary flower pushing vulnerably from a crack in parched earth, Centac's chances of survival in the tradition-bound bureaucracy were uncertain indeed"), big enough for the other.

Mills describes his adventure with Centac as "a five-year odyssey through a labyrinthine underground world I believe no journalist ever before traveled end-to-end, a meticulously filligreed web of passages within which hums and clatters a multibillion market of drugs, assassins, weapons, and spies. It was a world of diplomats, statesmen, global politics, and crime, where everything could be bought for cash -- lives, armies, the governments of nations."

Wow! But let's go on. "Centac became at once a lens through which to view that Empire, and a vehicle to take me to its center, face to face with its leaders, their wives and lovers, into their mansions and yachts, their banks and counting rooms, to a secret wonderland of wealth so vast it threatened the economic stability of the world."

I don't remember accompanying Mills to all those places, but he did do an awful lot of leg work and interviewing. My only quibble is that most of those he got his information from were, necessarily, drug agents and drug dealers (turned stool) who were doubtless eager to impress this writer with what romantic chaps they were -- "free spirit people," as one dealer put it to Mills.

The book revolves around Centac's efforts to build conspiracy cases against three organizations -- "one led by a wealthy, homicidal power-obsessed Cuban homosexual named Alberto Sicilia-Falcon, another by a young American entrepreneur named Donald Steinberg (a man with criminal operations on four continents and a daily income greater than U.S. Steel's), and a third masterminded by a rumpled, retiring -- and murderously ruthless -- Chinese named Lu Hsu-shui . . . whose global power included ties to a three-thousand man drug army and the intelligence services of at least three nations."

YOU'RE GOING to have to get used to superlatives. Mills is apparently a product of the Sax Rohmer school of writing -- "the largest, most sweeping criminal investigation in history," "the most menacing criminal groups in the world." There are no ordinary cops and criminals here. One drug soldier is "a stone cold diabolical psychotic killer" who moves "with the stealth and skill of a jungle cat." A stoolie named the Fatman "has the mind of a fox, the ethics of an alley cat, and the quick-kill instincts of a rattlesnake." Dealer Lu Hsu-shui is "wary as a cobra" and moves "with speed and cunning in the twisted passageways of . . ." Mills looks into the eyes of a Colombian dealer and sees "quietly revealed a mind educated to cunning, eager to locate deceit, ready in an instant to murder."

Sometimes, I have to admit, I get the feeling Mills is exaggerating, as when he says that a Centac agent, as remarkable as Mr. Memory in The 39 Steps, "had been digging away at the Steinberg empire for more than a year, had committed all the investigation's files to memory. Names, dates, addresses, phone numbers, license plate numbers, bank account numbers, aircraft registrations, ship names, corporate histories -- he carried it all in his head."

I won't give away the conclusions of the three investigations except to say that Director Dennis Dayle's boast, "We can do anything," turned out to be wrong. Still, along the way the Centac chases provide Mills with many good anecdotes, some glossy profiles, some stuff that, as he admits, is kind of hard to believe. But when the topic is drugs, who insists on credibility?

You will like the tunnelling escape from prison in Mexico, and the Jimmy Valentine opening of a safe in South Florida. If your taste is People magazine, you will go for the rumors that place a female federal magistrate in bed with the attorney for drug merchants. (Is that why she kills cases on technicalities?) And you will enjoy the slapstick evidence that a drug king's life is not all Maserati cars and Dom Perignon champagne.

The bad news is the poundage. It reminds me of that recent New Yorker cartoon: a publishing house executive, referring to the mound of manuscript on his desk, says to the author, "I'm sorry we can't be more encouraging, but allow me to add that you've got a hell of a lot of book here."

A good writer/good reporter has been seduced and betrayed by his own diligence. Mills collected "hundreds of pages of classified documents, 183 two-hour tape cassettes (these eventually produced more than 7,000 pages of transcription), and 22 notebooks" -- and he fell fatally in love with too much of it. After trimming and discarding tons of stuff, he just didn't have the heart to cut the remaining ton by 50 percent, which would have left it a first-class book instead of a chore to get through.