WASHINGTON—HBO has been broadcasting a compelling documentary on Barry Goldwater, the father of modern American conservatism. The film is a stark reminder of the fascinating challenge that present-day America poses to the conservative mind.

The five-term Republican senator famously defeated by Lyndon Johnson’s ruthless presidential campaign in 1964 had staunch beliefs and was more interested in being consistent than in being persuasive or pleasant. So he was unpopular, except for those 3 million or so of the faithful who kept his cause alive—a movement that brought about Ronald Reagan and, later, George W. Bush.

The documentary, produced by Goldwater’s granddaughter, reminds us that the Arizonan was in favor of small government not only in economic matters but also on moral issues. In that respect, he exposes the inconsistency of conservatives who pay only lip service to small government and to those who are for small government in economic matters but think the state should impose their moral values on others. Goldwater really wanted to reduce government intrusion in people’s lives. “My aim is not to pass laws, but to repeal them,” he wrote in “The Conscience of a Conservative.” That meant reducing taxes and spending, and also eliminating moral diktat.

His many critics in the Republican Party called him “dishonest” and “maverick” for supporting a woman’s right to an abortion and opposing discrimination against gays. There was nothing “maverick’’ about this. We may agree or disagree with his views, but it is only fitting for someone who thinks the government should not invade a person’s sphere to believe that high taxes and moral impositions are two forms of the same evil.

Not many conservatives, not even today’s “Goldwater conservatives,’’ realize this. But some do. George F. Will makes many interesting points in the documentary on how Goldwater’s vision deviates from present-day conservatism and its attempts to force the social order to conform to its values.

By any measure, the size of government has increased under the conservative Bush administration and a Republican-controlled Congress. Since 2001, federal outlays have gone up by 45 percent. The federal government has also grown in power: The fact that a Republican White House should favor a constitutional amendment banning gay marriage is indicative of the moral authority current conservatives assign to the federal government. For them, the premise of the Constitution—limiting the power of government—is less important than the moral imperative.

This contradiction, I would suggest, is one of the two great challenges modern-day America poses to a young conservative mind. The other one is the tension between the passion for limiting government and the belief in military intervention abroad—the warfare state. This is a contradiction to which Goldwater himself succumbed. He believed in mobilizing the juggernaut of government against ideological enemies abroad—hence his support for U.S. involvement in Vietnam—at the same time that he advocated limiting government in every other respect. Unlike so many Goldwater critics, I don’t think this was dishonest. It was a genuine contradiction at the heart of the conservative mind.

When the Cold War passed, many libertarians and conservatives found common cause because it looked like the warfare state would go away. But events, especially 9/11, have proved that hope wrong. And so conservatives find themselves today in an ideological trap: They want to defend taxpayers from too much government at home and save civilization through the expansion of government abroad, thereby expanding the very government they want to limit. Many current problems, including the tension between security and civil liberties regarding action against potential terrorists, arise from that intellectual ambivalence. If we add to this the contradiction between small economic government and big moral government, we can see how conservatives face an agonizing set of dilemmas.

This wasn’t always so. An astounding generation of American writers who rose up intellectually against Franklin D. Roosevelt in the 1930s and ‘40s brought together the three elements that tear apart present-day conservatism. They believed that citizens had the prime responsibility for their well-being, their moral values and their relation to other countries. Some call them the Old Right, though they did not use that term. They eventually waned and the Cold War saw the emergence of the new type of conservative—all the way to the interventionist neocons of today.

The issue is not academic. It translates into policy and has consequences for Americans as well as for millions around the world. Meanwhile, government continues to grow on all three fronts: spending, moral intervention and foreign assertion. At which point does a new conservatism begin the task of clearing the confusion?