The House majority leader, Representative Tom DeLay of Texas, rejected a demand from the administration that the House pass the Senate bill, which would provide an increased child tax credit to 6.5 million low-income families.

"Ain't going to happen," Mr. DeLay said this afternoon, reiterating his stance that the credits would be approved only as part of a much larger tax-cut bill, an $82 billion package that House Republicans unveiled later in the day and plan to bring to the floor on Thursday.