By RACHEL SWARNS

WASHINGTON - The government workers greeted Michelle Obama like a Hollywood celebrity, whooping and cheering. But when she took to the podium, the nation’s self-described mom in chief quickly turned to policy.

The first lady pitched her husband’s economic stimulus package, including plans to create 15,000 affordable housing units, weatherize 2 million low-income homes and repair military housing. Such investments, Mrs.Obama told employees at the Department of Housing and Urban Development, would prevent“an increase in homelessness during these tough economic times.”

In her first weeks in the White House, Mrs.Obama has been the gracious hostess and loyal spouse. But Mrs.Obama has also begun promoting bills that support her husband’s policy priorities.

In January, Mrs.Obama celebrated the enacting of a pay-equity law with a reception for women’s advocates at the White House. Recently, she supported the economic stimulus bill on her visit to the housing agency and another to the Department of Education.

Mrs.Obama’s aides said she relished the chance to serve as one of the president’s chief surrogates on critical policy matters.

“One of the things she does really well is to highlight the benefits of pieces of legislation,”said Jackie Norris, Mrs.Obama’s chief of staff.“She’s really kind of laying out things that are important to the administration. I think she’ll play an active role in supporting the president’s agenda.”

It is a notably different approach than the one embraced by the former first lady, Laura Bush, who steered clear of discussing legislation. Some observers praised Mrs.Obama’s foray into the legislative debate, saying the new first lady, who is a Harvard-educated lawyer and a former hospital executive, was eminently qualified to promote the president’s policies.

Others expressed surprise, saying they had expected Mrs.Obama to focus on her daughters and on the traditional issues she had emphasized in the presidential campaign, like supporting military families and working parents. Her remarks, they said, carried echoes of former first lady Hillary Rodham Clinton, though Mrs.Obama has said she will not become involved in policymaking as Mrs.Clinton did.

“She went to some lengths to say she was going to be first mom in chief,”Myra Gutin, a scholar of first ladies at Rider University in New Jersey, said of Mrs.Obama.“I don’t think we ever really imagined her edging toward public policy like this. It’s not like she’s making public policy. But it’s a little less neutral than some of the other things she’s talked about focusing on.”

Marcia D.Greenberger, co-president of the National Women’s Law Center here, countered that Mrs.Obama was successfully balancing her ceremonial role as first lady, her role as a mother and her keen interest in public policy.

“It seems like a combination of responsibilities that fit very naturally with who she is,”said Ms.Greenberger, who attended the signing of the pay-equity law at the White House.“You don’t have a sense that being a mom and being human and being able to understand everybody’s daily struggles has to come at the expense of her intelligence, her expertise and her understanding of the issues.”