WASHINGTON, Sept. 20 — President Bush, bracing for a series of battles with Congress over spending, threatened today to veto a bill expanding a popular children’s health insurance program, calling it “a step toward federalization of health care.”

The program expires Sept. 30, and Congress is on the verge of renewing it by providing coverage to an additional 4 million children over the 6.6 million already enrolled — at an additional cost of $35 billion over five years. Mr. Bush says the bill would expand a program aimed at helping the poor beyond its original intent.

The veto threat is just one of nearly a dozen the White House has issued recently aimed at a variety of bills including measures on education spending and money for medical research. With the fiscal year ending Sept. 30, Mr. Bush and Congressional Democrats are headed for a showdown over spending similar to the one that preceded the government shutdown of 1995.

On Capitol Hill, lawmakers have yet to complete action on any of their 12 major spending bills. But even if they do, Mr. Bush will not sign them; he has issued veto threats on 10 of the 11 appropriations measures passed so far by the House.