DENVER, June 21 - Backed by the unusual endorsement of 48 Nobel laureates, Senator John Kerry on Monday accused the Bush administration of letting ideology trump science, and promised to lift the limits on federal financing of stem-cell research and to build an economy "based on innovation, ingenuity and imagination."
Mr. Kerry and his scientific supporters echoed a 38-page report issued in February by the Union of Concerned Scientists, which accused the administration of "manipulation, suppression and misrepresentation of science" on issues like biotechnology, global warming and nuclear power.
Mr. Kerry vowed to "listen to the advice of scientists" and make their advisory reports open to the public. The group of scientists had complained that the White House heavily edited a report by the Environmental Protection Agency to remove almost any finding pointing to a human link to global warming.
Mr. Kerry also invoked the recent death of President Ronald Reagan from Alzheimer''s disease and echoed Nancy Reagan''s call for stem-cell research "to tear down every wall today that keeps us from finding the cures of tomorrow."
"We need a president who will again embrace the tradition of looking toward the future and new discoveries with hope based on scientific facts, not fear," Mr. Kerry, the presumptive Democratic presidential nominee, told thousands of people here at Civic Center Park, many of whom waited for hours on a rainy 50-degree day to see him.
"Presidents are supposed to think big and dream big and help our nation to do so," he said, citing Franklin D. Roosevelt''s creation of the national laboratories, John F. Kennedy''s commitment to put a man on the moon, and Bill Clinton''s support for mapping the human genome. "When America sees a problem or a possibility of greatness, it is in our collective character to set our sights on the horizon and not stop working until we get there," Mr. Kerry said.
On Monday night, Mr. Kerry decided to upend his schedule, canceling a fund-raiser and speech on Tuesday in New Mexico to allow him to fly back to Washington overnight for a possible vote on an amendment to make health care financing for veterans mandatory. Mr. Kerry has rarely interrupted his campaign activities for Senate business, but veterans'' health care is a signature issue in his campaign.
Burton Richter, who received the Nobel in physics in 1976 for discovering a subatomic particle and who helped Mr. Kerry''s campaign collect his colleagues'' support over the last 10 days, told reporters that "Nobel laureates tend not to use their names for anything outside of science," adding, "I hope you take that as a sign of how seriously all of us think the errors of our present course are."
Mr. Kerry''s speech, beginning a week focused on science and technology, was his first public appearance in Colorado, a Republican-leaning state that the Democrats hope to win. He noted, as he has in television advertisements, that he was born at an Army hospital nearby. It also reflected his increasing attention to stem-cell research, an issue for which Democrats believe they have public support.
Steve Schmidt, a spokesman for Mr. Bush''s re-election campaign, did not respond to the criticism of the president''s policy prohibiting research on stem cells harvested since his order in 2001. The issue has split his party, with many Republicans signing on to legislation to lift the limits, particularly since Mr. Reagan''s death. Mr. Schmidt answered the attack by pointing out that 22 of the 48 Nobelists who signed the pro-Kerry statement also signed a statement in January 2003 opposing war in Iraq, and 16 had given money to Democratic candidates.
In addition, 13 of the 48 were part of the group that released the February report criticizing the administration''s approach to science.
"Only John Kerry would declare the country to be in scientific decline on a day when the country''s first privately funded space trip is successfully completed," Mr. Schmidt said in a statement, referring to the rocket plane SpaceShipOne''s journey 62 miles from earth and back.
Mr. Schmidt said the administration had increased the budget for research and development 44 percent since 2001, to $132 billion next year, and pointed to the president''s plans to develop hydrogen fuel cells, promote clean coal technologies and modernize the electricity grid.
The Union of Concerned Scientists charged that the administration had often dismissed experts or selected others for scientific advisory panels based on their views on contentious subjects. The Bush administration has called most of the accusations made in the organization''s report inaccurate and has said that the E.P.A. draft on global warming was dropped because more voluminous reports on climate change were in the works.
But in a conference call, three of the scientists supporting Mr. Kerry said that Mr. Bush had let America lag behind Europe and Asia in terms of patents, advanced degrees and publications in scientific journals.
"Where are the new things of tomorrow going to come from?" Dr. Richter asked. "This isn''t about what''s going to happen next week, it''s what''s going to happen next decade."
Harold Varmus, who won the Nobel Prize in medicine in 1989 for his discovery of the cellular origin of retroviral oncogenes and headed the National Institutes of Health under President Clinton, accused the Bush administration of taking a "cavalier attitude in the way it receives advice from the scientific community." Mario J. Molina, a 1995 Nobel laureate for his work in atmospheric chemistry, said he was concerned that Mr. Bush "overplays politics to scientific information."