Tourists who go abroad to abuse children should face the prospect of prosecution in their home countries if they are caught having sex with kids in nations with lax penalties, participants at a U.N.-backed conference concluded Friday.

Sweden already has such a law, and about 3,000 experts plus government representatives from 137 nations backed the concept at the Third World Congress against Sexual Exploitation of Children and Adolescents in Rio de Janeiro.

Their final declaration called for nations to establish laws allowing stiffer prosecution of child sex cases for perpetrators who take trips to nations with few or no penalties because they know they'll face little if any retribution, said Nils Kastberg, UNICEF's director for Latin America and the Caribbean.

"Many of these pedophiles tell each other, 'Oh, don't worry if something happens to you in that country, the worst that will happen is you'll pay a fine,'" Kastberg said in a telephone interview. Participants are now expected to go to their home countries and lobby governments for the law changes.

They also supported the creation of detailed sexual abuse databases in nations around the world so that governments can find out the extent of sexual exploitation of children beyond just the sex trade. Armed with that information, they can work to solve problems ranging from child prostitution, sexual abuse of children by people ranging from family and friends to priests. The International Labor Organization estimated at least 1.8 million girls and boys under age 18 were involved in the global sex trade in 2000, and nobody knows how much it has grown since then.

But a recent U.N. survey estimated that 150 million girls and 73 million boys under age 18 were forced to have sexual intercourse or experienced other forms of sexual violence in 2002. "It is very hard to know the true size of the problem, said Geoffrey Keele, a spokesman for UNICEF, a congress co-sponsor. "Only things that are known are budgeted and planned for. We're going to try to get governments to do in depth studies in this area, might take funding from UNICEF or donors to get it going."

Brazil is a sex tourism destination with long-standing child prostitution problems involving both foreign and Brazilian clients. President Luiz Inacio Lula da Silva signed a decree just before the congress began this week that boosts the minimum child pornography prison sentence from two to four years.