WHAT exactly are we fighting for? In his speech to the nation on Wednesday, President Bush said it was to "defend our freedom" and "bring freedom to others." Nowadays, Americans always go to war under the banner of freedom, ours or theirs: Operation Iraqi Freedom follows Operation Enduring Freedom in Afghanistan.

There was a time when the campaign would have been fought in the name of liberty. The recent efforts to rebaptize French fries as "freedom fries" contrast with the World War I renaming of sauerkraut as "liberty cabbage" and dachshunds as "liberty dogs." Freedom fries may have owed something to alliteration, but liberty was much more prominent in the patriotic lexicon back then than it is now. Americans bought liberty bonds and planted liberty gardens; factories turned out liberty trucks and liberty aircraft engines.

If it ever came to all that today, it's a safe bet that we would be talking about freedom bonds and freedom trucks. For that matter, a modern patriot who was writing the Pledge of Allegiance from scratch would probably conclude it "with freedom and justice for all."

This shift from liberty to freedom is a subtle one, which few other languages would even be able to express. The French national motto is usually translated as "Liberty, equality, fraternity," but liberté could as easily be translated as freedom.

Even in English, the words can sometimes seem to be equivalent. The philosopher Isaiah Berlin used them more or less interchangeably in his essay "Two Concepts of Liberty," and so did the historian Eric Foner in his "Story of American Freedom," which traces the evolution of the concept from Colonial times. Indeed, the words are often incanted in the same breath. "The issue is freedom and liberty," Mr. Bush said a few days before the war began. Or as the Grateful Dead said, "Ooo, freedom/ Ooo, liberty/ Ooo, leave me alone."

But English hasn't taken the trouble to retain all those pairs of Anglo-Saxon and Latin near synonyms just so its thesauruses could be heftier. There's a difference between friendship and amity, or a paternal manner and a fatherly one.

Liberty and freedom are distinct, as well. As the political theorist Hanna Fenichel Pitkin has observed, liberty implies a system of rules, a "network of restraint and order," hence the word's close association with political life. Freedom has a more general meaning, which ranges from an opposition to slavery to the absence of psychological or personal encumbrances (no one would describe liberty as another name for nothing left to lose).

But the two words have been continually redefined over the centuries, as Americans contested the basic notion of what it means to be free. For the founders of the nation, liberty was the fundamental American value. That was a legacy of the conception of "English liberty," with which Britons proudly distinguished themselves from the slavish peoples of the Continent who were unprotected from the arbitrary power of the state. Echoing John Locke, the Declaration of Independence speaks of "life, liberty and the pursuit of happiness." The text doesn't mention freedom at all. It was liberty that Patrick Henry declared himself willing to die for, and liberty that the ringing bell in Philadelphia proclaimed on July 8, 1776.

Liberty remained the dominant patriotic theme for the following 150 years, even if freedom played an important role, particularly in the debates over slavery. Lincoln's Gettysburg Address began by invoking a nation "conceived in liberty," but went on to resolve that it should have a "new birth of freedom."

But "freedom" didn't really come into its own until the New Deal period, when the defining American values were augmented to include the economic and social justice that permitted people free development as human beings. Of Roosevelt's Four Freedoms — of speech, of religion, from want and from fear — only the first two might have been expressed using "liberty.'

The civil rights movement made "freedom now" its rallying cry. The Rev. Dr. Martin Luther King Jr. used "freedom" 19 times in his "I Have a Dream" speech, and liberty only twice. Feminists extended freedom to cover reproductive rights, while Timothy Leary spoke of the "fifth freedom . . . the freedom to expand your own consciousness."

But as Professor Foner has observed, freedom is too central in the American consciousness to remain the property of one political side. The conservative reclaiming of the word began during the cold war, when it was expanded to include the benefits of free markets and the consumer choices they provided. Then, too, freedom was a conveniently vague label used to describe free-world allies like Franco's Spain, whose commitment to liberty was questionable.

President Ronald Reagan understood the power that "freedom" had acquired. His second Inaugural Address mentioned freedom 14 times and liberty only once. But in the mouth of Mr. Reagan and other conservatives, freedom conveyed what Isaiah Berlin called its negative sense, an absence of constraints on markets and individual action. Mr. Reagan's program of "economic freedom" included deregulation, tax cuts and a weakening of unions, which earlier conservatives had championed in the name of the "liberty of employers."

The invocation of freedom became as reflexive for the right as it had been for New Deal Democrats and those in the civil rights movement. Opponents of civil rights legislation appealed to "freedom of association," and opponents of affirmative action have spoken of "freedom from race." On the National Rifle Association's Web site, the word freedom is three times as frequent as the word liberty.

But as the expanding use of "freedom" makes every policy and program a part of the national mission, "liberty" has receded from the patriotic vocabulary. If we still venerate the word now, it's less as a rallying cry than as a stand-in for the legalistic niceties that the founders took such trouble over. That's why the word still comes up when the conversation turns to the domestic war on terrorism, whether in the expression "civil liberties" or standing alone.

Lately, Bush administration figures have been trying to wrest the word from the critics of their homeland security measures.

When a special appeals court upheld the wiretap provisions of the USA Patriot Act a few months ago, Attorney General John Ashcroft called the decision "a victory for liberty, safety and the security of the American people." And last week, the secretary of homeland security, Tom Ridge, announced Operation Liberty Shield, which will step up surveillance of those suspected of terrorist ties and authorize indefinite detention of asylum-seekers from certain nations.

BUT many still hold that liberty and safety, like guns and butter, are notions that are more appropriately opposed than conjoined. They're mindful of Benjamin Franklin's warning that "they that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." Right now, "Iraqi Freedom" conveys something more basic than "American freedom" suggests — it is simply emancipation from tyranny, not a choice of S.U.V.'s or an end to double taxation of dividends. The Iraqis may someday enjoy those more advanced varieties of freedom. Ultimately, they may even enjoy liberty. But that will require more time, and as we have had ample opportunity to learn, eternal vigilance.

Copyright 2003 The New York Times Company. Reprinted from The Sunday New York Times, Week in Review, of March 23, 2003.