WASHINGTON— Companies that hire the unemployed would claim new tax breaks under a jobs-promoting bill that's expected to pass the Senate today.

It's the first of several jobs bills promised by Democrats, and passage would give President Barack Obama and Majority Leader Harry Reid, D-Nev., a much-sought victory. But the measure's impact on hiring is likely to be relatively modest, economists say.

The bill up for a vote today would exempt businesses hiring the unemployed from the 6.2 percent Social Security payroll tax through December and give them an additional $1,000 credit if new workers stay on the job a full year. It would also extend federal highway programs through the end of the year and make a $20 billion cash deposit into the highway trust fund to make up for shortfalls from lower-than-anticipated gasoline tax revenues.

Reid's $35 billion proposal — blending $15 billion in tax cuts and subsidies for infrastructure bonds issued by local governments with the $20 billion in highway money — is a far smaller measure than the $862 billion economic stimulus bill enacted a year ago.