Washington  - US President Barack Obama will nominate Kansas Governor Kathleen Sebelius as health secretary on Monday, his second choice for what will be a critical post in the new administration, according to US media reports.

Sebelius, who was once considered a possibility for vice president, will take the job after Obama's first pick Thomas Daschle was forced to withdraw amid a tax scandal.

Obama has vowed to reform the US health care system, one of the costliest in the world, during his first term. The challenge has frustrated previous administrations due to sharp ideological differences over how to tackle the problem.

More than 40 million people in the United States do not have health insurance.

During the 2008 election campaign, Obama supported a public- private system. He suggested creating a government-run insurance option to compete alongside private insurers, in order to expand access and pull down costs.

Republicans have already signalled strong opposition, fearing the idea will eventually lead to a government-dominated health care system similar to those in Britain or France.

Sebelius, 60, was elected governor of the Midwestern state of Kansas in 2003 and re-elected in 2006. She previously headed the state agency that regulates insurance companies.

Sebelius' nomination as head of the Health and Human Services Department fills Obama's last remaining cabinet nomination. She will still have to be approved by the US Senate.

Daschle, a former Senate majority leader and close friend of Obama's, chose to withdraw his nomination after it emerged that he had failed to pay more than 100,000 dollars in taxes on a private car and driver. dpa