President Bush has vowed to veto the legislation, saying it goes beyond the program's original goal of covering low-income children and is a first step toward nationalized health care. Instead, he has proposed an increase of $5 billion over five years to the program's current $25 billion funding level.
The State Children's Health Insurance Program is set to expire Sept. 30.
The Senate bill would provide enough funding to add 3.2 million children to the program, which already covers more than 6 million children nationwide. It would pay for the measure by raising taxes on cigarettes from 39 cents per pack to $1, and by cutting payments to private managed-care plans under Medicare.
The program is designed to cover children whose families earn too much money to qualify for Medicaid, but not enough to afford private health insurance. Each state sets its own income limits to qualify for the program, and in some states it has expanded to cover middle-income children and some adults, mostly parents.
The Senate vote came a day after the House voted 225-204, largely along party lines, to approve the $50 billion program expansion.
"This is the children's hour," House Speaker Nancy Pelosi, D-Calif., said Wednesday. "We are able to meet our moral obligation to children."
The House and Senate plan to meet after their August recess to reconcile the differences between the two bills before sending a final measure to President Bush.
The Senate passage of 68-31 -- with 18 Republicans joining 48 Democrats and 2 independents -- is enough to override a presidential veto, but the House's vote is not.
Senate Minority Leader Mitch McConnell, R-Ky., backed the president, saying the legislation's supporters "have seized the reauthorization of SCHIP as a license to raise taxes, increase spending and take a giant leap forward into the land of government-run health care."
But not all Republicans agreed. "It's difficult for me to understand how anyone wouldn't want to do this," said Sen. Orrin Hatch, R-Utah.
Hatch and Sen. Edward Kennedy, D-Mass., told the Washington Post Tuesday that House-Senate negotiations will aim to keep the final bill within the scope of the Senate's measure to try to avoid a veto.