"Ultimately ... the buck stops here," the Republican speaker said, using the phrase of a Democratic president, Harry Truman.
Hastert held to his assertion that he did not know about ex-Rep. Mark Foley's e-mails and sexually explicit computer messages to former pages until the scandal broke last week.
The ethics committee promised to finish its investigation in weeks, not months, but it was unclear whether that would occur before the Nov. 7 election. Hastert's handling of the issue has brought harsh criticism from some fellow Republicans and conservative activists.
An AP-Ipsos poll found that about half of likely voters say recent disclosures of corruption and scandal in Congress will be very or extremely important. That group is much more likely to vote Democratic.
The speaker, at a news conference, mixed a newfound contriteness with defiance.
"Could we have done it better? Could the page board have handled it better? In retrospect, probably yes. But at the time what we knew and what we acted upon was what we had."
But he also vowed to win re-election and run for House speaker again.
Privately, Republicans say that Hastert's mea culpa was the very least he could do, but they're far from sure it will be enough, CBS News correspondent Gloria Borger reports. On the record, they're trying to be upbeat.
"Hopefully he's cleared the air so members and challengers can have this off the front pages of the paper," Rep. Ray Lahood, R-Ill., told Borger.
Meanwhile, President Bush called Hastert to thank him for how he has handled the situation. The White House says that Mr. Bush praised Hastert for "making a clear public statement that said the House leadership takes responsibility and is accountable."
While the Committee on Standards of Official Conduct — the ethics committee — is investigating potential violations of House rules, the Justice Department appeared to be moving with dispatch in its criminal investigation.
Timothy Heaphy, a lawyer for ex-Foley chief of staff Kirk Fordham, said his client had just met with the FBI. Fordham emerged as a key figure Wednesday when he told reporters that he had talked three years ago with top aides to Hastert about Foley's conduct with pages. His comments pushed back the time when information may have reached the speaker's office.
CBS News correspondent Sharyl Attkisson reports that the FBI also visited former page Tyson Vivyan, who said Foley sent him sexually charged instant messages, but only after he left the page program. He told CBS News the messages were "referencing genitalia, referencing specific acts between the two of us, things like that."
Since Vivyan wasn't a minor, the FBI told him it didn't appear Foley had violated any laws in his case.
Ethics committee chairman Doc Hastings, R-Wash., and ranking Democrat Howard Berman of California would provide no details on the subpoenas but told a news conference the committee was seeking both testimony and documents.
Hastert spokesman Ron Bonjean said the speaker had not yet received a subpoena from the ethics committee but was willing to testify. "If the ethics committee asks him to, of course," Bonjean told The Associated Press.
Several lawmakers and aides could logically be summoned, based on what is known so far. The committee also could subpoena former lawmakers and staff, including Foley, a Florida Republican, and Fordham. However, the House has no authority to punish anyone no longer a member of Congress or an employee.
According to public statements and an internal review by Hastert's office, a likely list of those who had some involvement in events and could be summoned include: Hastert aides Tim Kennedy, Mike Stokke, Ted Van Der Meid and Scott Palmer; former Clerk of the House Jeff Trandahl; Rep. Rodney Alexander, R-La., who became aware that Foley sent questionable e-mails to a page he sponsored; Rep. Tom Reynolds, R-N.Y., who spoke with Alexander about Foley; Majority Leader John Boehner; and Rep. John Shimkus, R-Ill., chairman of the board that oversees the page program.
Hastings and Berman, in an unusual procedural move, said they will personally lead the investigation, joined by Reps. Judy Biggert, R-Ill., whose district adjoins Hastert's, and Stephanie Tubbs Jones, D-Ohio. Their investigative subcommittee thus has two Republicans and two Democrats.
"We pledge to you that our investigation will go wherever the evidence leads us," Hastings said.
Berman said the committee did not consider suggestions from congressional watchdog groups and editorial writers to name an outside counsel. He said the committee could do the job without partisanship.
"We have, we all have strong feelings about party, about issues, about philosophy. But for purposes of this investigation, those feelings are irrelevant. And I think that's all that the chairman and I are trying to say," Berman said.
The White House tried to distance President Bush from any political backlash from the page sex scandal Thursday, saying House Republicans were dealing with the matter and don't need to be told what to do.
Bush has not talked with Hastert or other members of the House GOP leadership, presidential spokesman Tony Snow said.
Hastert announced that a tip line had been activated for people to call if they have information on Foley or any problems with the page program. The number is 866-348-0481.