Four days after Barack Obama did it, Hillary Rodham Clinton has gone on the air in Pennsylvania.

Clinton's campaign announced yesterday that it had begun running a television commercial called "Level" across the state.

Sources familiar with the extent of Clinton's advertising said her buy for the coming week was less than half the size of Obama's and was focused primarily in the Philadelphia market. Her statewide ad buy appeared to be in the range of $600,000, his about $1.6 million.

The Clinton commercial, which includes scenes shot in workplaces and has a strong blue-collar feel, portrays her as a friend of the middle class who wants to end tax breaks for companies that ship jobs overseas.

"Standing up for people who weren't getting a fair shake, that's been the purpose of my life," she says in the ad. "And it will be the purpose of my presidency."

The same ad ran in Ohio during the final days before its March 4 primary. Clinton won that contest, defeating Obama by 10 percentage points.

Clinton's Pennsylvania effort also got a boost yesterday from EMILY's List, the Washington-based organization committed to electing more Democrats, especially women. Its Women Vote! project announced it would contact 150,000 Democratic women on Clinton's behalf in five congressional districts surrounding Philadelphia.

Those contacts, to be made through recorded telephone calls and mailings, are to begin in early April with the goal of increasing women's turnout.

In Ohio, women represented 59 percent of those voting, according to the exit polls. In virtually every contest, Clinton has run better among women than among men, sometimes by 10 percentage points or more.

Maren Hesla, who runs the Women Vote! effort, said what voters "see in Sen. Clinton is someone who's better able to take on the issue that causes them the most concern, the economy."

The group has worked for Clinton in primaries in New Hampshire, New Jersey, Texas and Ohio.

In a poll done last week for EMILY's List, Clinton led Obama 48 percent to 35 percent among likely Pennsylvania Democratic primary voters. It found her ahead among women by 22 percentage points and trailing among college-educated men by 25 points.

Obama, who took a break from campaigning to spend time with his family, returns to Pennsylvania Friday for a six-day bus tour starting in Pittsburgh and ending next week in the Philadelphia area.