Worst excuse ever.

WASHINGTON — Representative Nancy Pelosi of California, the House Democratic leader, reversed course on Wednesday and said she would not back changes to a 2008 law that gave certain undocumented immigrant children broader legal rights to enter the United States.

Ms. Pelosi had suggested this month that she could accept changes to the Bush-era law that would expedite the deportation of children in exchange for President Obama’s emergency $3.7 billion request to deal with a sudden surge of unaccompanied minors at the border, mainly from Central America.

Since then, she said, Republican leaders have given little indication that they will back that funding request. One of her own members, Representative Henry Cuellar, Democrat of Texas, teamed up with Senator John Cornyn, Republican of Texas, this week to introduce legislation that would amend the 2008 law, which is intended to stop sex trafficking, but which grants migrant children from Central America extra legal protections that have made them harder to return quickly to their home countries.

The Democratic leadership’s hard line raises the prospects of an impasse on Capitol Hill that leaves the Obama administration with no additional resources to deal with the border surge. Republican leaders have said they will not give the president a “blank check” without policy changes. The Congressional Hispanic Caucus was set to meet with Mr. Obama on Wednesday afternoon, and White House officials were to brief Democratic senators on the border issue in the evening.

Ms. Pelosi, in an interview on Wednesday, said she had spoken with Mr. Cuellar, and suggested it was not a friendly conversation.

“I do think the bill that was introduced is exactly the wrong way to go,” she said. “Is the only immigration bill we’re going to have one that hurts children?”

She said the Congressional Hispanic Caucus had united against any bill that changes the way children migrants are treated. The rest of the House Democratic caucus will follow the Latino lawmakers’ lead, she said.

“This crisis is an opportunity to demonstrate who we are as a country,” Ms. Pelosi said.