WASHINGTON (AP) – The House ethics committee opened an expansive investigation into the unfolding page sex scandal Thursday, approving nearly four dozen subpoenas for witnesses and documents as House Speaker Dennis Hastert held his ground against pressure to resign.

“I’m deeply sorry this has happened and the bottom line is we’re taking responsibility,” Mr. Hastert, R-Ill., told at a news conference outside his district office.

“Ultimately, the buck stops here,” the speaker said of the controversy enveloping the House, Rep. Mark Foley and the page program, a venerable institution almost as old as the Congress itself.

Mr. Hastert was abruptly changing the tactics he has followed since the scandal broke last week in the wake of the disclosures and Mr. Foley’s resignation. He since has entered an alcohol rehabilitation facility in Florida. As recently as Wednesday, Mr. Hastert had blamed Democrats for the scandal and insisted he had done nothing wrong.

The committee’s chairman, Rep. Doc Hastings, R-Wash., said a newly formed subcommittee’s investigation “will go wherever our evidence leads us.”

Asked if embattled Mr. Hastert was among those subpoenaed, Mr. Hastings would not comment. Mr. Hastings said the subpoenas cover lawmakers and staff as well as appointed officers of the House.

Mr. Hastert’s spokesman Ron Bonjean said the speaker has not received a subpoena from the ethics committee but was willing to testify. “If the ethics committee asks him to, of course,” Mr. Bonjean said.

The committee’s senior Democrat, Rep. Howard Berman of California, said the investigation should take “weeks, not months.”

Mr. Hastert praised the ethic committee’s actions and said he would instruct his attorney to cooperate with the panel “in getting to the bottom of this.”

“The committee is moving to get control of this situation and find answers to provide all of us peace of mind,” he said in a statement earlier.

“Any person who is found guilty of improper conduct involving sexual contact or communication with a page should immediately resign, be fired, or subjected to a vote of expulsion,” Mr. Hastert said.

Mr. Hastert was asked about Mr. Foley’s former chief of staff saying in an interview with The Associated Press that he had talked three years ago with top aides in the speaker’s office about Mr. Foley’s behavior with pages.

“You know, it’s interesting,” Mr. Hastert said. “Kirk Fordham also said just about three or four days ago that he worked for this guy for 10 years and he never did anything wrong. So there’s a little bit of difference in the testimony or what he said.”

Mr. Hastert was said by officials in advance of the speaker’s news conference to have planned to ask a former FBI Director, Louis Freeh, to also examine the page system and make recommendations. But that did not immediately materialize, and Mr. Hastert did not broach the name at his news conference.

Congressional aides said Mr. Hastert called House Minority Leader Nancy Pelosi, D-Calif., to suggest Mr. Freeh, but that Ms. Pelosi objected.

Mr. Hastings said the subpoenas cover lawmakers and staff as well as appointed officers of the House.

As Mr. Hastert huddled with aides earlier Thursday, the ethics panel opened its investigation into Mr. Foley’s computer-message advances to teenage congressional pages and accusations – even by some Republicans – that House leaders failed to protect the teens.

The swift-moving developments came as a furor mounted over the revelations about Mr. Foley and his resignation last Friday. Negative fallout for Republicans struggling to keep control of Congress was apparent in the latest AP-Ipsos poll, conducted this week after the Foley revelations surfaced.

About half of likely voters said recent disclosures of corruption and scandal in Congress will be very or extremely important in their vote next month, and Democrats enjoyed a nearly 2-to-1 advantage as the party better able to fight corruption.

Some leading Republicans have publicly blamed Hastert for failing to take action after he was warned about the messages. And a former Foley aide said he told Republican leaders about the Florida congressman’s conduct years earlier than they have acknowledged.

With Republicans concerned about maintaining their congressional majority in the elections, support for Mr. Hastert was ebbing. Republican officials said at least a few disgruntled members of the Republican rank and file had discussed whether to call on the speaker to step aside. The officials spoke on condition of anonymity, citing the sensitivity of the issue.

In Atlanta, meanwhile, former page Tyson Vivyan, now 26, told AP he received sexually suggestive computer messages in 1997, years before the communications exposed last week, from an anonymous sender who turned out to be Mr. Foley.

Mr. Foley’s attorney, David Roth, declined to comment.

Mr. Hastert announced that a tip line had been activated for people to call if they have information on Mr. Foley or any problems with the page program. The number is 866-348-0481.

The Justice Department earlier this week ordered House officials to preserve all records related to Mr. Foley’s electronic correspondence with teenagers. The request for record preservation is often followed by search warrants and subpoenas, and signal that investigators are moving closer to a criminal investigation.

Mr. Foley, 52, stepped down after he was confronted with sexually explicit electronic messages he had sent teenage male pages. He has since entered an alcohol rehabilitation facility at an undisclosed location. Through his lawyer, he has said he is gay but denied any sexual contact with minors.