European government are trying to ensure the deal will not violate their strict privacy laws, a legacy of the continent's history with authoritarian regimes.
"I think the value of this data perhaps is not widely understood. You can't have an informed discussion on how to handle it unless you know what it is that it provides," Chertoff told The Associated Press after a meeting on terrorism with top security officials from Europe's six largest nations.
Chertoff has cited the case of an agent at O'Hare airport in Chicago who, unsatisfied with a foreign traveler's responses, refused him entry and took his fingerprints in June 2003.
Those fingerprints, according to Chertoff, turned up later on the steering wheel of a suicide truck bomb detonated in Iraq.
The European Union and United States must hash out an agreement to replace one that expires in July to avoid potential problems for passengers and airlines.
Among the disagreements are how long American authorities should be able to use data about passengers on trans-Atlantic flights, when it should be destroyed and which agencies should have access. The United States also wants the authority to pull data directly from airline computers, but European countries insist airlines must transmit the information.
Chertoff met bilaterally with European counterparts on the sidelines of the Venice conference, and will press his message in meetings with EU parliamentarians in Brussels next week.
"What I hope to do in that visit is to explain, with some detail how valuable that information is to us, using examples of cases in which we have stopped people or intercepted people coming into the country who are terrorists or drug traffickers," he said.
European countries also are concerned about U.S. plans to strengthen its visa waiver program - including requiring participating countries to join the passenger data sharing agreement.
"Common sense tells you in the end we shouldn't be duplicating things, we should be harmonizing them," Chertoff said.
The EU is pressing the United States to extend the visa-waiver program to all countries in the bloc. Citizens from 15 of the 27 EU nations can enter the United States and stay up to 90 days without applying for a travel visa. But Greece and most of the newer EU members fail to meet criteria for joining the program.
Americans, meanwhile, can travel to every EU country without visas.
Legislation pending in Congress would allow the program to admit new countries, while requiring all participating countries to impose closer scrutiny of their passports to ensure they are not lost, stolen or easily counterfeited.
President Bush has said he favors adding countries to those already on the visa-waiver list, all but four of which are European.
Turning to security threats, Chertoff said Homeland Security has not changed its threat status in response to a potential terror plot against U.S. military bases in Germany. The suspected plot was first made public in an April 20 warning to U.S. diplomatic and consular facilities in Germany to increase security.
"I would say that we are in the posture that we are normally in. We recognize there is a threat that remains out there," Chertoff said.
He called the arrests last week of six foreign-born Muslim men suspected of plotting to massacre U.S. soldiers at Fort Dix, N.J., a "vivid example of that." He declined to comment further on the case, saying it was ongoing. Chertoff said he wasn't aware of any specific threats against the upcoming Group of Eight meeting in Germany, and expressed confidence in that country's ability to secure the event. "Obviously, when you get a group of leaders together ... security is a very important part of what goes on, whether it be terrorism or people who want to disrupt the proceedings," Chertoff said. "I am confident that the Germans will be very focused on and very skilled at making sure there is adequate security." AP-CS-05-12-07 1339EDT