WASHINGTON >> Facing calls to resign, Veterans Affairs Secretary Eric Shinseki said Thursday that he hopes to have a preliminary report within three weeks on how widespread treatment delays and falsified patient scheduling reports are at VA facilities nationwide, following allegations that up to 40 veterans may have died while awaiting treatment at the Phoenix VA center.

Shinseki resisted calls from a Democratic senator to bring in the Justice Department and FBI for a criminal investigation. Shinseki said he first wanted to see results of the audit and a report on the VA inspector general’s office on its investigation of the Phoenix hospital.

Sen. Richard Blumenthal, D-Conn., said there appears to "solid evidence of wrongdoing within the VA system" that could be criminal.

"It’s a pattern and practice, apparently, of manipulating lists and gaming the system — in effect, cooking the books, creating false records," Blumenthal said, adding that the VA’s inspector general lacked the proper resources to pursue a criminal investigation.

"The more I learn about the misconduct and impropriety at the VA medical facility, the more concerned I am there’s evidence of criminal wrongdoing," said Blumenthal, a former state attorney general and federal prosecutor.

Shinseki said he is "mad as hell" over allegations of treatment delays and preventable deaths at a Phoenix veterans hospital and vowed to hold employees accountable for any misconduct.

"Any adverse event for a veteran within our care is one too many," Shinseki said at a Senate hearing Thursday on the Phoenix allegations and other problems at the VA. "We can, and we must do better."

Shinseki’s testimony marked his first extended comments since allegations surfaced last month that the Phoenix VA hospital maintained a secret waiting list to hide lengthy delays for sick veterans. A former clinic director says up to 40 veterans may have died while awaiting treatment.

Some Republicans and veterans groups have called for Shinseki to resign.

Pushing back against sometimes hostile questions, Shinseki said he welcomes a White House review of his beleaguered department. "If allegations about manipulation of appointment scheduling are true, they are completely unacceptable — to veterans, to me and to our dedicated VA employees," he said.

The hearing before the Senate Veterans Affairs Committee comes as President Barack Obama has assigned White House deputy chief of staff Rob Nabors to work on a review focused on policies for patient safety rules and the scheduling of patient appointments. The move signaled Obama’s growing concern over problems at the VA. Problems similar to those that surfaced in Phoenix have since been reported in other states.

Sen. Patty Murray, D-Wash., said the hearing "needs to be a wake-up call for the department," noting that outside reviews have outlined problems with wait times and quality of care since at least 2000.

"It’s extremely disappointing that the department has repeatedly failed to address wait times for health care," Murray said.

Murray told Shinseki she believes he takes the allegations seriously and wants to do the right thing, "but we have come to the point where we need more than good intentions."

Murray called for Shinseki to take "decisive action to restore veterans’ confidence in VA, create a culture of transparency and accountability and to change these system-wide, years-long problems."

Sen. John McCain, R-Ariz., said the Obama administration "has failed to respond in an effective manner" to allegations made public more than a month ago. "This has created in our veterans’ community a crisis of confidence toward the VA — the very agency that was established to care for them," McCain said.

A White House official said Shinseki requested more help with the VA review, leading Obama’s chief of staff, Denis McDonough, to tap Nabors for the assignment. Shinseki said he welcomed Nabors’ help, noting that he served with Nabors’ father, like Shinseki a retired Army general.

"While we get to the bottom of what happened in Phoenix, it’s clear the VA needs to do more to ensure quality care for our veterans," Obama said in a statement.

The chairman of the Senate committee said there were "serious problems" at the VA but lawmakers must avoid a rush to judgment.

"I don’t want to see the VA system undermined," Sen. Bernie Sanders, I-Vt., told The Associated Press. "I want to see it improved. I want these problems addressed."

"If people are cooking the books, running second books, that is wrong. That’s illegal and we have to deal with it," Sanders said, adding he also was troubled by reports that some veterans have to wait up to six months to see a doctor.

The VA system is the largest health care system in the country, serving nearly 9 million veterans a year at 152 hospitals and more than 1,500 other sites nationwide. Surveys show patients are mostly satisfied with their care. But with such a huge system, "there are going to be problems," Sanders said.

The House Veterans Affairs Committee voted last week to subpoena all emails and other records in which Shinseki and other VA officials may have discussed destruction of what the committee called "an alternate or interim waitlist" for veterans seeking care in Phoenix. A top VA official had told congressional staff last month that the "secret list" referred to in news reports may have been an "interim list" created by the hospital.

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Associated Press writer Pauline Jelinek contributed to this report.