LAS VEGAS (Reuters) - Amid growing worries about a worsening of the U.S. economy, Democratic presidential candidate Barack Obama proposed a $75 billion economic stimulus plan on Sunday that includes worker tax credits, a one-time pension supplement and help to homeowners facing foreclosure.

The plan would include an immediate $250 tax credit to workers that could double if the economy worsens, a one-time $250 supplement to Social Security payments, a $10 billion fund to help homeowners facing foreclosure and a $10 billion fund to bolster states facing budget shortfalls amid lower tax revenues.

"We need that middle-class tax cut now more than ever -- not five months from now or five weeks from now, but now," Obama said in a statement. "I'm announcing a plan to jump-start the economy by putting money in the pockets of those who need it most and will spend it quickly."

The Illinois senator's office unveiled the proposals at the start of a day of campaigning in Nevada, which holds the next contested Democratic primary on Saturday.

His leading rival, New YorkSen. Hillary Clinton, on Friday unveiled an economic stimulus package she said would be worth $70 billion. Her plan placed more of an emphasis on helping families unable to make mortgage payments -- a major issue in Nevada where "for sale" signs are common on homes across Las Vegas, its major city.

The plan also includes a $10 billion extension of unemployment insurance to help those who have been unable to find a job for more than half a year.

Last year, the senator proposed tax credits of up to $500 for 150 million workers. His revised economic plan calls for $250 of that to come in an immediate credit, and the rest as soon as three months later if the nation's unemployment rate worsens.

(Editing by David Wiessler)