WASHINGTON — President Bush said Thursday that the House Democrats' version of a terrorist-surveillance bill would undermine the nation's security and that he would veto it.

The House is expected to vote on the measure later Thursday. Bush went before cameras before the vote to encourage Democrats to drop their effort.

Bush says the House version "would cause us to lose vital intelligence on terrorist threats" and would not give liability protection against lawsuits to telecommunications companies that cooperated with the government after the Sept. 11 terrorist attacks.

Bush prefers the Senate-passed version of the measure, which would grant legal immunity to the telecommunications firms. He said lawsuits against telecommunications companies would lead to the disclosure of state secrets. Further, he said it would undermine the willingness of the private sector to cooperate with the government in trying to track down terrorists.

Directing his message at the House, Bush said, "They should not leave for their Easter recess without getting the Senate bill to my desk."

He said the Senate would not pass the House version of the bill, and even if the Senate did, he would veto it.

"Their partisan legislation would extend protections we enjoy as Americans to foreign terrorists overseas," the president said.

Nineteen Democrats on the House Judiciary Committee issued a statement on Wednesday challenging the administration's arguments.

"We have concluded that the administration has not established a valid and credible case justifying the extraordinary action of Congress enacting blanket retroactive immunity as set forth in the Senate bill," they said in a statement issued by the committee chairman, Rep. John Conyers, D-Mich.

They said they have seen no evidence that suits have harmed the telecommunications companies' reputations or finances, or that intelligence gathering has been compromised.