WASHINGTON  President Obama on Saturday described his expansive budget proposal as “a threat to the status quo in Washington” and cast himself as a populist crusader willing to do battle with special interests to expand health care, curb pollution and improve education.

“I didn’t come here to do the same thing we’ve been doing or to take small steps forward,” Mr. Obama said in his weekly radio and Internet address. “I came to provide the sweeping change that this country demanded when it went to the polls in November. That is the change this budget starts to make, and that is the change I’ll be fighting for in the weeks ahead.”

The address hinted at the strategy the White House intends to employ to push for the spending plan released last week, a return to a more traditional Democratic approach of positioning the party as fighting against the rich and powerful. In Mr. Obama’s telling, he is taking on entrenched interests in the form of banks, insurance companies, large agribusinesses, oil and gas companies and others.

Beyond the $3.6 trillion budget for the 2010 fiscal year, the president’s spending plan outlines an array of ambitious initiatives for the next several years that collectively would transform American society. He wants to extend health coverage to the more than 40 million uninsured, revamp industry so that it stops producing so many emissions that cause climate change, develop alternative energy sources and invest billions of dollars more in education.