Holdren, a professor of environmental policy at Harvard University, led the Pugwash Conferences on science and world affairs, an international organisation of prominent scientists that won the Nobel Peace Prize in 1995.

Holdren is not new to Washington, having served as science and technology adviser to then president Bill Clinton in the 1990s.

Obama called Holdren "one of the most passionate and persistent voices of our time about the growing threat of climate change".

Genetic research priority

Underscoring the importance of genetic research, Obama named Eric Lander and Harold Varmus as co-chairmen of the council of advisers alongside Holdren.

Lander is founding director of the Broad Institute, which played a leading role in the Human Genome Project which in 2003 succeeded in mapping the location of about 20,500 genes on the 23 pairs of human chromosomes.

Lander and his colleagues are using these findings to explore the molecular mechanisms underlying the basis of human disease, a field that could hold the key to curing many incurable diseases, Obama aides said.

Varmus, a co-recipient of a 1989 Nobel prize for studies of the genetic basis of cancer, has been serving as president and chief executive of Memorial Sloan-Kettering Cancer Centre in New York since January 2000.

Obama expressed confidence that together the two men will "remake" the "group into a vigorous external advisory council" that will shape his thinking on scientific aspects of his policies.

Radio address

In a weekly radio address, Obama said: "It's time we once again put science at the top of our agenda and worked to restore America's place as the world leader in science and technology.

"Today, more than ever before, science holds the key to our survival as a planet and our security and prosperity as a nation."

From landing on the moon, to sequencing the human genome, to inventing the Internet, America has been the first to cross that new frontier, he said.

Obama said that government had played an important role in encouraging those breakthroughs and could do so in the future.

Commenting on Obama's science and climate appointments, Todd Kent, a professor of political science at Texas University in Qatar, told Al Jazeera: "He doesn't want the continual focus on the economy [which is in recession]. I think he chose a Saturday address to focus on something else. One is policy and one is politics.

"President Bush used stem cell research and and his anti-abortion stance to really keep the right wing of his [Republican] party in check, and I think what Obama is going to do is to use environment issues to keep the left wing of his [Democratic] party in check."