Democratic presidential hopeful John F. Kerry, taking aim at President Bush's science policy, promised Monday that he would overturn a ban on federal funding of new stem cell lines, saying that as president he would be guided by "science . . . not ideology."

Beginning a week in which Kerry will speak about his science initiatives, the Massachusetts senator's campaign touted his endorsement by 48 Nobel Prize-winning scientists, who issued a letter saying Kerry would "restore science to its appropriate place in government and bring it back to the White House."

Kerry, speaking to a rain-soaked crowd at a downtown park, said he would increase funding for the National Institutes of Health, the National Science Foundation and the Energy Department to promote more scientific research. He did not offer specifics.

Kerry was making his first campaign trip to Colorado as the presumptive Democratic nominee. He flew here from a weekend stop at his vacation home in Nantucket, Mass., and attended a luncheon in the ski resort town of Aspen, where he raised $500,000.

Colorado has been a Republican stronghold, but Kerry hopes to make an issue of job losses in the state during the past four years.

Kerry suggested Monday that the country's leadership in science and technology was in doubt, citing "reports" that other countries are investing more in research. "America," he said, "has been losing its lead."

Steve Schmidt, a spokesman for the Bush campaign, disputed that characterization, saying that "only John Kerry would declare the country in scientific decline on a day when the country's first privately funded space trip is successfully completed. America is the world leader in patents, research and development and Nobel Prizes."

Schmidt said Bush's 2005 budget calls for $132 billion in research and development funding, which he said was a 44 percent increase since Bush took office.

Kerry said that more than 100 million Americans have illnesses and injuries, including heart disease and cancer, that could be cured or treated with therapies derived from stem cell research. He specifically cited former first lady Nancy Reagan's support for stem cell research. Her husband, former president Ronald Reagan, had Alzheimer's disease.

Stem cell research has remained controversial because it relies, in part, on cells from destroyed human embryos. The Bush administration has permitted research and experimentation on some existing cell lines but has heeded religious groups that have raised ethical and moral concerns about developing new ones.

Kerry seemed to suggest that his administration would pursue a more liberal policy. "We must lift the barriers that stand in the way of stem cell research and push the boundaries of medical exploration so that researchers can find treatments that are there, if only they are allowed to look. And we should do this while providing strict ethical oversight. . . . It's about investing in the future of our country. And when I am your president, I won't let ideology and fear stand in the way."

In another development Monday, Vernon E. Jordan Jr., an adviser to former president Bill Clinton, officially joined the Kerry campaign as the lead debate negotiator. Jordan said he took the job because wants to see a "change in leadership" at the White House.

In his new role, Jordan will wrestle with a Republican counterpart over where the candidates will stand, who will speak first or last and which moderators will ask the first questions. Negotiators will work with the Commission on Presidential Debates.

"I think I have a responsibility not only to John Kerry but also to the American people to have a debate on issues and information that educates the electorate as opposed to entertaining the electorate," he said.

Jordan said he first considered a role in the campaign last week, when the candidate asked.

"I'm a good Democrat," he said. "And I'm ready for change, absolutely."

Staff writer Darryl Fears contributed to this report.