Democratic presidential candidate John Kerry (search) criticized President Bush's replacement of two dissenting members of a bioethics panel that advises him on such issues as cloning and stem cell research.

"A scientific panel ought to be chosen on the basis of science and on the basis of reputation, not politics," the Massachusetts senator told reporters Saturday during a refueling stop on a flight from Oakland, Calif., to New York.

"I think that is the wrong thing to do when a country is searching for its appropriate scientific policy. We deserve to have people whose reputations and abilities are not tarnished and are not focused by politics or religion."

Elizabeth Blackburn, a cell biologist at the University of California at San Francisco and former president of the American Society for Cell Biology (search), and William F. May, a medical ethicist and retired professor at Southern Methodist University, were dismissed Friday from the President's Council on Bioethics.

Bush created the council in 2001, replacing a similar commission that advised President Clinton, to tackle issues including embryonic stem cell research, euthanasia and assisted reproduction. He named its 17 members to two-year terms in January 2002.

Elizabeth Marincola, executive director of the American Society for Cell Biology, a nonprofit group representing basic biomedical researchers, said Blackburn and May were often in the minority on the council as they provided dissenting views.

In their place, Bush named Benjamin Carson, director of pediatric neurosurgery at Johns Hopkins Children's Center in Baltimore; Peter Lawler, chairman of the Department of Government and International Studies at Berry College in Georgia; and Diana Schaub, a political science professor at Loyola College in Maryland.

The White House did not respond directly to earlier allegations that Blackburn and May were replaced for ideological reasons.

Suzy DeFrancis, a spokeswoman for Bush, said that since their terms had expired in January, it was the president's "prerogative to make changes." All the council's members' terms expired in January.

"We decided to appoint other people with other expertise and experience," she said, without elaboration.

Some Christian and politically conservative groups oppose the research — especially through stem cells created by cloning embryos in labs — as immoral because fertilized embryos must be destroyed to harvest the cells.

Many stem cell scientists say the policy severely restricts research that could benefit millions of patients.

As to his own view, Kerry said: "I'm against human cloning. I'm against other irresponsible scientific activities."

He said he favors cell research, but "there are limits to how the lines are developed and there are limits to what you do. Absolutely. But again, you look for the best scientific and bioethical advice. You don't precook it. That's what's important."