George Bush yesterday used his presidential veto for only the fourth time in seven years to block legislation that would have given health insurance to millions of poor American children.

He announced his opposition to the expansion of an existing insurance program last month. The exercise of his veto power yesterday isolates the White House on the most pressing domestic issue for many Americans, and puts Mr Bush in conflict with Congress, where there was widespread Republican support for the legislation.

The legislation would have extended health cover to 10 million poor children, and would have cost $60bn (£29.5bn) over the next five years. It had widespread support outside Congress, from state governors and even the health insurance industry.

The White House argued that the program represented a stealth effort to bring in government health care, and would have extended coverage to middle class families as well as the poor. ” This legislation would move health care in this country in the wrong direction,” Mr Bush said yesterday. ” Under this bill government coverage would displace private health insurance for many children.”

Democrats said the veto demonstrated Mr Bush’s detachment from the American mainstream. ” The same president who is willing to throw away a half trillion dollars in Iraq is unwilling to spend a small fraction of that amount to bring health care to American children,” said Edward Kennedy, senator from Massachusetts.

Republicans feared the veto could hurt their prospects in next year’s elections.