WASHINGTON — President Bush said yesterday that the House Democrats’ version of a terrorist-surveillance bill would undermine the nation’s security and that if it reaches his desk, he would veto it. Ratcheting up his rhetoric, Mr. Bush said, “The American people understand the stakes in this struggle. They want their children to be safe from terror.”

The House was expected to vote on the measure late yesterday. Mr. Bush went before cameras on the South Lawn before the vote to encourage Democrats to drop their effort and, instead, support a Senate-passed version.

Replying to Mr. Bush, Senator Kennedy, a Democrat of Massachusetts, said the president was trying to bully Congress and mislead the people.

“He refuses to accept that under our system of government, neither the president nor the telecommunications companies gets to decide which laws to follow and which to ignore,” Mr. Kennedy said in a written statement.

The law is intended to help the government pursue suspected terrorists by making it easier to eavesdrop on foreign phone calls and e-mails that pass through America. The law expired February 16 after Congress did not quickly renew it. Mr. Bush said the House bill “could reopen dangerous intelligence gaps by putting in place a cumbersome court approval process that would make it harder to collect intelligence on foreign terrorists.”

The Senate-passed version would grant legal immunity to the telecommunications firms. Mr. Bush 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, Mr. Bush said, “They should not leave for their Easter recess without getting the Senate bill to my desk.”