President Bush this morning vetoed a bill that would renew and expand the state-federal health insurance program for low-income children, delivering on his threat to block a measure he has said is too costly and could lead to excessive government control of the health-care system.

Bush vetoed the measure shortly before leaving this morning on a brief trip to Lancaster, Pennsylvania, where he was planning to speak to business leaders about his efforts to hold the line on federal spending. The White House has sought to make fiscal discipline a broad element of its legislative strategy this fall.

Bush appears to have the votes to sustain his veto, the fourth of his presidency, in the House, but Republicans have warned the White House that Bush is endangering the party's political prospects in 2008.