WASHINGTON — The Treasury Department's inspector general wants Treasury to explain its secretive process for deciding which banks receive investments of taxpayer dollars from the government's $700 billion financial rescue program.

The inspector general's office is looking at Treasury's decision to invest $400 million in Beverly Hills, Calif.-based City National Bank as "a case study in the process by which financial institutions apply and are selected," spokesman Richard Delmar said.

A report will be published in the next few months, he said.

The study comes amid rising criticism from lawmakers that Treasury is making decisions without a public, clear and consistent rationale. Treasury Secretary Henry M. Paulson Jr. announced in October that the department would invest $250 billion in healthy banks.

So far, Treasury has invested in all but one of the 25 largest banks, including Citigroup, whose financial problems have since required a doubling of the original federal investment. Several smaller banks with financial problems also have received investments from the Emergency Economic Stabilization Act. Central Pacific Financial, based in Honolulu, was approved on the same day it disclosed that regulators had ordered it to raise more capital. The bank said it would use the taxpayer dollars to comply with the regulatory order.

"The public must be able to clearly understand the factors Treasury is relying upon to make the decision," Sen. George V. Voinovich, R-Ohio, wrote to Paulson in mid-December, after the Post reported the details of the Central Pacific investment. "If ailing banks are receiving assistance from the EESA to meet regulatory requirements, then the intent of the program has certainly changed."

Delmar emphasized that the inspector general's office did not select City National for its case study because of concerns about the institution's health.

"It is not a reflection at all on the bank's safety or soundness," he said.

He would not comment on why the bank was chosen for the case study, which was first reported by the Los Angeles Times.

The bank, whose customers include many Hollywood luminaries, received the $400 million from Treasury Nov. 21.

City National is reasonably healthy by current standards. Its income dropped by 73 percent in the third quarter, but it made a profit. Its capital foundation is larger than required by regulators, much larger after the Treasury investment.

A bank news release described the government's investment as "a strong vote of confidence in City National." The bank now highlights the investment in a banner on its Web site that advertises, "Stability in volatile times."

"All we know about this review is what we've read in the press," a bank spokesman said. "We take at face value the statement of the Treasury Department's inspector general."

Treasury has described its selection process only in the broadest terms, most recently in a letter it sent Wednesday answering questions from a panel appointed by Congress to oversee the use of the rescue funds. The letter said applications are reviewed by the federal agency that regulates the bank. The agency makes a recommendation. And Treasury makes a decision.

The letter added that consistent standards govern the process but did not describe the standards.