More people have been arrested in recent years for sexually soliciting youths online, but the sharp increase comes from better enforcement, and the Internet remains a relatively safe social environment, researchers said in a new study.

In a report to be released Tuesday, the researchers saw a nearly fivefold jump in arrests for soliciting undercover investigators who posed as juveniles — to 3,100 in 2006, from 644 in 2000, the last time the study was conducted.

By contrast, arrests for solicitations of actual children increased 21 percent to about 615 in 2006, from an estimated 508 in 2000, during a period in which Internet usage also grew sharply.

The disparity indicates that the rise in arrests largely results from tighter enforcement rather than from an increase in the number of offenders, said David Finkelhor, director of the University of New Hampshire's Crimes Against Children Research Center, which conducted the study. Otherwise, he said, the rate of growth for the two groups would be more similar.

Throughout the decade, the federal government helped fund Internet Crimes Against Children Task Forces across the country, while some states have updated their laws to address online solicitations.

The large increase in arrests shows that such efforts are working, said John Palfrey, an Internet safety expert at Harvard University who was not involved in the study.

"The law enforcement community should take pride in the fact that they are doing some things right," said Palfrey, who recently headed a task force charged with assessing technologies for protecting children from unwanted contact online.

The New Hampshire center's data from 2000 have been widely cited in Internet safety circles, but they predate the popularity of social networks such as News Corp.'s MySpace. In providing the update, the researchers are hoping to assuage fears parents may have about their children spending time in such online hangouts.

Researchers did see solicitations shift from chat rooms, where children used to be propositioned most frequently, to online social networks, as young people spend more time there. But the researchers found no evidence that minors were being lured by predators based on the personal information they post. Rather, they said, youths often were actively seeking relationships with people they knew to be adults.

The researchers also say that the arrests of online predators in 2006 represent just 1 percent of all arrests for sex crimes against minors, which declined overall.

Both sets of arrest figures represent estimates from mail and telephone surveys with more than 2,500 law-enforcement agencies. The 2000 study was based on arrests from July 1, 2000, to June 30, 2001, while the 2006 data were for that calendar year.

A small number of individuals were arrested for both soliciting an undercover agent and a child; those cases were included only in the total for youths.