As the rift widens between the United States and Europe over war with Iraq, a new book offers an explanation. Robert Kagan's Of Paradise and Power, says the United States has grown more assertive, while Europe much less so. With a literary flourish, Mr. Kagan says it's a matter of Mars versus Venus, god of war versus the goddess of love. His thesis has aroused much debate on both sides of the Atlantic.

Scoffing at U.S. intransigence on Iraq, French Foreign Minister Dominique de Villepin told The Washington Post newspaper, ?One must be coherent. One must be logical. One must have sang-froid. One must not enter into things in an ideological mode.?

A perfect expression of the European mind today, author Robert Kagan might say. His new book, Of Paradise and Power, contrasts peace-addicted Europe with militarily assertive America.

A senior associate at the Carnegie Endowment for International Peace, Mr. Kagan says Europe and America hardly occupy the same world any more.

Having succeeded in ending centuries of warfare among themselves, European nations are now basking in peace and prosperity, writes Mr. Kagan. They want others to copy their skills at negotiation and reconciliation. No need to fight, they say, if it can be avoided.

That means letting others -- namely, the United States -- fight for them, writes Mr. Kagan. He says they enjoy the good life and much diminished defense spending under U.S. protection, for which they show little appreciation and even contempt.

Europe and the United States have indeed diverged on matters of defense, says Simon Serfaty, Director of European Studies at the Center for Strategic and International Studies in Washington.

?What is true, as Mr. Kagan does point out, is that there has been a widening gap in military capabilities between the United States and the states of Europe,? Mr. Serfaty says. ?And this gap has grown so immense since September 11 as to make the European states relatively incapable in terms of their capacity for contributing to any sort of military action.?

The United States did not seek the role that has been thrust upon it, says Mr. Kagan. America is a behemoth today, but with a conscience. It wants to spread its values to the rest of the world, if necessary by timely military action.

Mr. Serfaty offers a word of caution.

?Military power gets you into a conflict and helps you win the conflict. It is necessary,? he says. ?But it is not sufficient to end the conflict and to make sure it is not repeated soon after the war has been won. There is a certain congruity between the nature of American power and European power, which Kagan does not touch upon.?

Don't even mention power to Europeans, writes Mr. Kagan. They believe they have transcended it. That depends on the kind of power you are talking about, says Mr. Serfaty.

?If you do limit power to the sole military dimension, then indeed the United States is strong and everybody else is weak,? he says. ?However, power clearly extends far beyond its military dimension, and the alternative to power is not weakness but order because the European states, the allies, are very strong in a number of areas including diplomatic, political, economic, financial and in the area of intelligence.?

In fact, says Mr. Serfaty, Europeans want to restrain America with institutions like NATO and the United Nations that have tamed their own nationalisms. Some even call America the rogue nation most to be feared today.

This is the strategy of the weak, says Emilio Viano, professor in the School of Public Affairs at American University in Washington. By choice, Europeans have disarmed themselves.

?They really do not have the military capability. They spend much less than the United States on their own military, and they have no intention of spending more,? Professor Viano says. ?This in a way has created their own economic and social and political miracle, because under the umbrella of U.S. protection and leaving it up to the U.S. to spend and invest in the military, they have the time, money and the means to pay more attention to their quality of life.?

Since the collapse of the Soviet Union, the United States does not enjoy that luxury, says Professor Viano. Entrusted with military defense of an otherwise disarmed West, it must be assertive, as Mr. Kagan suggests.

?Therefore, it sees threats and solutions to such threats in a different way from Europe, which does not have those military capabilities and thus has to look for other avenues for solutions and is more amenable to think of international law, negotiation, seduction, containment than an intervention that they cannot afford,? he says. So there is a trade-off, says Professor Viano. Europeans get a touch of paradise, Americans something less.

?We in the United States may relish the power but have to pay for it through a lower quality of life, while Europeans may have to eschew power and accept a secondary role, but in the end maybe win in the sense that they live better, so to speak, always counting on our support and protection should any military problem develop,? Professor Viano says.

Mr. Serfaty says Mars has not really been tested. While ready for war, the United States may not be prepared for casualties. Americans quickly pulled out of Lebanon in 1984 and Somalia in 1994 when their troops were killed. What will be their staying power in Iraq?

?The French, for example, suffered more casualties in Bosnia and Kosovo than we the United States did in the 1990's,? he says. ?I would think that the totality of European casualties through the use of force in the 1990's far exceeds the totality of U.S. casualties in the context of military engagements over the past 10 to 12 years.?

Mr. Serfaty says under intense military pressure, Mars might begin to look like Venus. In any U.S. war, he says, there must be a sense of necessity and a perception of success.

Professor Viano agrees that Venus may not be quite so passive as author Kagan thinks. Europeans have learned patience from adversity. They take pride in the methods they have evolved for dealing with crises. If Americans talk of their mission, so do Europeans. It is forging a unity of once fractious nations.

?We have even been able to integrate the most threatening of them all - Germany - into our community without firing a single shot since World War Two, mainly by diplomacy and by taking a kind of technical approach, an approach basically that looks very bureaucratic, not very exciting, starting with a trade zone and then moving on progressively to a political integration,? he says.

Professor Viano says Americans are understandably reacting to the horror of the September 11 attack on their homeland. Yet over the centuries, Europeans have suffered many similar catastrophes.

?They have experienced destruction. They have experienced famine,? he says. ?They have experienced total chaos, and therefore they take a more blasé attitude in saying we can live with threats. We can live with some uncertainty. We can live with indefinite kinds of situations.?

Professor Viano says threats can be forever, and Venus will continue to contend with Mars over how to deal with them.