Those figures have drawn contempt from European critics. “The U.S. pursues the war on drugs with an ignorant fanaticism,” said Ms. Stern of King’s College.

Many American prosecutors, on the other hand, say that locking up people involved in the drug trade is imperative, as it helps thwart demand for illegal drugs and drives down other kinds of crime. Attorney General Michael B. Mukasey, for instance, has fought hard to prevent the early release of people in federal prison on crack cocaine offenses, saying that many of them “are among the most serious and violent offenders.”

Still, it is the length of sentences that truly distinguishes American prison policy. Indeed, the mere number of sentences imposed here would not place the United States at the top of the incarceration lists. If lists were compiled based on annual admissions to prison per capita, several European countries would outpace the United States. But American prison stays are much longer, so the total incarceration rate is higher.

Burglars in the United States serve an average of 16 months in prison, according to Mr. Mauer, compared with 5 months in Canada and 7 months in England.

Many specialists dismissed race as an important distinguishing factor in the American prison rate. It is true that blacks are much more likely to be imprisoned than other groups in the United States, but that is not a particularly distinctive phenomenon. Minorities in Canada, Britain and Australia are also disproportionately represented in those nation’s prisons, and the ratios are similar to or larger than those in the United States.

Some scholars have found that English-speaking nations have higher prison rates.

“Although it is not at all clear what it is about Anglo-Saxon culture that makes predominantly English-speaking countries especially punitive, they are,” Mr. Tonry wrote last year in “Crime, Punishment and Politics in Comparative Perspective.”

“It could be related to economies that are more capitalistic and political cultures that are less social democratic than those of most European countries,” Mr. Tonry wrote. “Or it could have something to do with the Protestant religions with strong Calvinist overtones that were long influential.”