THE REIGN of President Samuel Kanyon Doe -- Africa's most appalling extant Big Man -- is coming to a messy end in Liberia.

A rebel army is advancing on the capital, Doe's ministers are buying one-way air tickets to Europe and the U.S. Marines are arriving to protect American interests.

Doe himself, who has presided over a decade of secret executions and public cannibalism, rigged elections and raging egotism, mass minting of "Doe dollars" and mass flight of financial institutions, now seems to see the darkness at the end of the tunnel.

In perhaps the last of his many inane proclamations, with rebels troops 30 miles from the capital, Doe told a press conference last week: "I wish to announce here today my firm decision not to stand for the 1991 general elections."

On the basis of his record, Doe deserves to be overthrown, perhaps even imprisoned for life. But what Americans should note is that our governnment was, in large measure, responsible for forcing the Liberian people to wait so long and suffer so much before a bad leader could be gotten rid of.

Liberia is the closest thing to a colony that the United States has ever had in Africa. The architecture echoes the antebellum South and spoken English has the rhythms of black American slang.

This relationship was never more "special" than under Doe. In the years 1980-85, Washington gave his government more than $500 million -- more aid per capita than to any country in Africa, more aid than it saw fit to give Liberia in the entire 133 years between the country's founding and the night in 1980 when Doe's colleagues eviscerated then-President William R. Tolbert.

For five years, the American taxpayer subsidized one-third of government spending under Doe.

The Reagan administration said it spent this money to protect American interests in Liberia (radio transmitters and airport landing rights) and to smooth a transition from military rule to elective government.

(It is probably unnecessary to add that President Reagan, himself, did not take a personal interest in Liberia. He once introduced President Doe at the White House as "Chairman Moe.") What Americans ended up buying was neither stability nor democracy. They paid for a brand of temporary legitimacy that has become a specialty of African Big Men: guns to coerce loyalty, money to rent it.

Doe, a skinny, unschooled backwoods master sergeant whom one American ambassador to Liberia called "an endearing boy," was more cunning than he looked. Repeatedly, he outfoxed the State Department.

He promised to return to his barracks, which he did not. He promised a free and fair election, which he rigged. He promised financial discipline, which he faked. For his every promise, the U.S. government rewarded him with aid. For his every betrayal, the U.S. government accepted another promise. Finally, under pressure from human rights groups and Congress, the cycle of Doe's bad faith and American generosity broke down.

A violent coup has seemed inevitable in Liberia for at least five years. Doe is the last of an almost extinct generation. He is an African Big Man who blends buffoonery with savagery while bankrupting his nation and turning his government into an international disgrace. Emeritus members of the club include Idi Amin of Uganda and Jean Bedel Bokassa of the Central African Republic.

Amin ordered white British citizens to carry him on a throne and encouraged his soldiers to murder an estimated quarter-million people. Bokassa threw himself a $22-million coronation and poisoned his own grandchild. Doe made his birthday a national holiday and told journalists that "no bullet can touch me, no knife can scratch me." He nodded in approval in 1985 when his soldiers -- after crushing a coup attempt -- cruised around Monrovia in a jeep displaying the coup leader's severed testicles. It was in the aftermath of the rigged election of 1985 that the Reagan administration had a chance to ease Doe out of power and save Liberians from five years of worsening misery. There was no doubt about what had happened in the election. Mounds of burned presidential ballots were discovered outside the capital. American diplomats in Monrovia detailed blatant and widespread election irregularities. The vote count, according to these diplomats, showed that Doe lost the election.

After phony results were announced, however, the Reagan administration chose "to go with Doe." Chester Crocker, Reagan's assistant secretary of state for African affairs, told Congress that "there is now the beginning, however imperfect, of a democratic experience . . . ."

Having watched the farce first-hand in Liberia, a number of American diplomats there were outraged by their government's acceptance of fraud. "It was one of those rare times when U.S. foreign policy could have made the difference," said one senior diplomat who served in Monrovia during the election. "We funded the election, we organized it, we supervised the voting, and then when Doe stole it, we didn't have the guts to tell him to get his ass out of the mansion."

The post-election passivity of the U.S government in Liberia contrasted markedly with tough American action five months later, in the wake of a similarly rigged election in the Philippines, to force out Ferdinand Marcos. Doe's dependence on the United States was such in 1985 that he, like Marcos, would have had no choice but to step down. That would have prevented the bloody coup attempt that followed the election.

Before Doe, Liberia was one of the few African countries without serious tribal hostility. But in the wake of the 1985 coup attempt, members of Doe's minority Krahn tribe took part in widespread killing, torture and humiliation of rival tribesman. The rebel movement that is soon to topple Doe is, in many ways, a continuation of the coup and tribal conflict that followed the stolen election.

Liberians, no doubt, are anxiously awaiting Doe's departure. He and his greedy advisers turned Liberia, a rubber-, timber- and iron-ore-producing nation of 2 million people, into an economic outcast. The three major multilateral lending agencies that specialize in doctoring sick African economies gave up on Doe and pulled out.

For the average Liberian, however, the tribal war has been worse than Doe's corrupt rule. More than 170,000 people have been forced to abandon their homes and farms. Thousands, perhaps tens of thousands, of people have been killed in the fighting and in tribal retaliation against Gio and Mano civilians by Krahn soldiers.

In the end, with Doe in prison or in exile or even carved up in pieces, Liberia will be a nation infected as never before by tribalism. And it will be led by someone it did not elect. The rebel leader, Charles Taylor, is a former Doe adviser who fled Liberia after being charged with embezzling $900,000 from the government. He does not speak about a need for immediate elections.

But he says he is looking forward to seeing what Washington is willing to do for his government. Having served in Doe's government, he no doubt knows that it was possible to receive a lot of money without having to answer a lot of questions.

"I would hope," Taylor said recently, "that we {Liberia and the United States} will have a really good marriage and a really good honeymoon."

Washington Post foreign correspondent Blaine Harden is currently "banned for life" from Liberia for earlier reporting. His book "Africa: Dispatches From a Fragile Continent" will be published in the fall by W.W. Norton & Co.