Who is more duplicitous, more inclined to deceive his own people as well as other nations for strategic advantage — current and past dictators such as Moammar Gaddafi, Hosni Mubarak and Saddam Hussein, or democratically elected Western leaders such as, say, Jimmy Carter, George W. Bush and Barack Obama?

Easy. Just look at Gaddafi, who early in the revolt against his regime claimed that the Libyan people still loved him, that the gunfire in his country was merely celebratory, and who announced a ceasefire only to continue his attacks on rebel forces. Or Mubarak, who tried to cling to power in Egypt by suggesting that nefarious foreign agents — rather than frustrated Egyptian citizens — were behind the Tahrir Square protests. It’s got to be the dictators, right?

John J. Mearsheimer would disagree. The University of Chicago political scientist argues that the leaders most likely to lie are precisely those in Western democracies, those whose traditions of democracy perversely push them to mislead the very public that elected them. In fact, Mearsheimer says, leaders tend to lie to their own citizens more often than they lie to each other.

In his disheartening yet fascinating book, “Why Leaders Lie,” Mearsheimer offers a treatise on the biggest of big fat lies, breaking down the deceptions the world’s presidents and generals and strongmen engage in — when, why and how they lie, and how effective those falsehoods can be.

First are “inter-state lies,” deceptions aimed at other countries to gain or retain some advantage over them. Think of Soviet Premier Nikita Krushchev grossly exaggerating the size of the Soviet Union’s ICBM arsenal — giving rise to the Cold War “missile gap” — in order to deter the United States from striking first. Or recall President Carter, whose press secretary had to lie to reporters at home when asked if the administration was preparing a rescue operation for the hostages in Iran. (Mearsheimer considers this an inter-state lie because the intended audience was Iran.) Or look at Greece, whose authorities misstated the size of the nation’s budget deficits in order to win admission to the European Union.

Such state-to-state lies are relatively uncommon, Mearsheimer contends, and successful ones are even less so. In a world where each state must fend for itself, leaders are unlikely to take each other’s word on serious stuff. (The world doesn’t buy Iran’s pronouncements that its nuclear program is peaceful, insisting instead that international inspectors verify the claims.) Also, if you lie too often, no one will trust you, so what’s the point?

Mearsheimer says that “fearmongering” — when leaders cannot convince the public of the threats they foresee and so deceive the people “for their own good” — is far more prevalent and effective. His Exhibit A is Bush and Iraq. With the public and Congress unconvinced of the case for war, “the Bush administration engaged in a deception campaign to inflate the threat posed by Saddam,” the author writes.

Mearsheimer, who opposed the invasion of Iraq on strategic grounds — he thought Saddam was dangerous but deterrable — calls out the administration on four falsehoods: Iraq’s possession of WMDs, the notion of a link between Iraq and al-Qaeda, the implication of an Iraqi role in the Sept. 11 attacks, and the suggestion that the administration was still seeking peace even on the eve of war.

Mearsheimer also points to President Lyndon Johnson and the infamous Gulf of Tonkin incident in 1964, which Johnson used to escalate the war in Vietnam; as well as to President Franklin Roosevelt’s lying about a 1941 skirmish between a German submarine and the U.S.S. Greer, an American destroyer — an event that FDR hoped would propel America into World War II. It is no coincidence that these are all freely elected leaders. Democratic regimes are more likely to fearmonger, Mearsheimer concludes, because, unlike dictators, they need public opinion on their side to go to war.

Next is the “strategic cover-up,” in which a leader misleads in order to cover up a policy that has gone badly wrong, or to hide a smart but potentially controversial strategy. Mearsheimer cites a French World War I commander so incompetent that French authorities hid his bungling, fearing it would undermine morale at home. He also recalls President Kennedy’s decision to deny that he had struck a deal with the Soviet Union to withdraw missiles from Turkey in exchange for Moscow pulling its missiles from Cuba. Whether or not the press believed it, Mearsheimer calls it “a noble lie, since it helped defuse an extremely dangerous confrontation between two states armed with nuclear weapons.”

The last two types of lies — “national mythmaking” and “liberal lies” — deal with a country’s self-perception. National myths fuel solidarity by putting a country’s history in the best possible light. This is why French schoolchildren read textbooks praising the country’s colonial past, or why America’s founders have achieved demigod status over the centuries. (Founding myths are particularly untrustworthy, Mearsheimer warns.) And liberal lies — a term the author uses apolitically — are used to justify odious behavior that conflicts with traditional ideals. For example, Winston Churchill and FDR served up a generous helping of deceit when depicting Stalin as a good guy (friendly ol’ “Uncle Joe”) to justify their cooperation with the Soviet leader during World War II.

To be clear, Mearsheimer doesn’t necessarily consider all this lying to be morally reprehensible. “There are sometimes good strategic reasons for leaders to lie,” he asserts. Depending on the situation, lies can be “clever, necessary, and maybe even virtuous.” But he does see some negative consequences to engaging in excessive deceit at the top.

Widespread lying makes it harder for citizens to make good choices in the voting booth, Mearsheimer writes, since they’ll often be working with false information. And in fragile democracies, pervasive lying can so alienate the public that they are willing to embrace more authoritarian leadership. Fearmongering and strategic cover-ups in particular are dangerous because they reflect leaders’ low opinion of (or even contempt for) the people they represent. Also, sometimes citizens refuse to support a war policy simply because they are intelligent and informed, and it is the leaders who have misread the threat. If so, lying to persuade the public leads to folly.

In the United States, of course, skepticism and mistrust of Washington already seem rampant, ranging from fringe conspiracies regarding Sept. 11 or President Obama’s birthplace to substantive debates on foreign and domestic policy. Rep. Joe Wilson’s infamous “You lie!” charge against Obama in 2009 was probably more shocking for its setting — a formal State of the Union address — than for its message.

And Mearsheimer worries that there will be more lying — and more mistrust — to come. Washington has proved adventurous in its foreign policy in recent years, willing to police the globe and use military force freely. And though the wars in Iraq and Afghanistan may dampen popular and elite enthusiasm for war, “it may not be long before the United States marches off on another crusade” — leaving leaders in Washington willing to fearmonger yet again in order to garner support.

Why do they do it? “They think that . . . what they are doing is for the good of the country,” Mearsheimer explains. “Thus their lies will matter little in the long run if they expose the threat for what it is and deal with it effectively.”

In other words, if you lie to start a war, make sure to win it.

Carlos Lozada is editor of Outlook.