Shares of Hanger Orthopedic Group Inc. plummeted yesterday after the Bethesda maker of mechanical body parts said second-quarter earnings will fall sharply lower than expected and stock analysts complained that the company did not fully explain why.

Executives said they were so busy cooperating with an investigation into an employee's allegations that Hanger overbilled patients and insurers that they were not able to release a second-quarter earnings report on Monday, according to a Securities and Exchange Commission filing late Tuesday.

Hanger said it now expects to release its earnings Monday.

In the filing, the company said pretax profit -- the only number it disclosed -- will be about $2.5 million in the three months ended June 30. Analysts had expected it to be between $13 million and $15 million. The company did not forecast profit for the second quarter in its last earnings report.

The lower earnings mean Hanger does not have enough cash to meet rules governing the amount it can borrow from its revolving credit line, it said. Hanger attributed the lower earnings -- a drop of 84 percent from a year ago -- to lower same-store sales, an increase in costs for materials and higher selling, general and administrative expenses. Hanger officials did not return calls yesterday.

The stock fell 41 percent yesterday following the filing, dropping $3.87 to close at $5.64.

The company said it had $14.6 million in cash Friday, and analysts said yesterday they were confident the company can resolve the debt issue. More troubling, the analysts said, is why the earnings shortfall was so great in what is usually a relatively stable business -- making and servicing prosthetic limbs.

"It was a substantial earnings miss," said Michael Petusky, who tracks the company for Thompson, Davis & Co., an investment firm in Richmond. Petusky personally owns shares of Hanger. "And we don't have a lot of detail on what factored into that."

"There's very little information available at this point to understand what happened," said Arnold Ursaner, an analyst at CJS Securities, an independent research firm in White Plains, N.Y. Ursaner also personally holds Hanger stock.

It has been a year of turmoil for Hanger, which has bought up smaller companies to consolidate what had been a fragmented industry. An employee in its West Hempstead, N.Y., office accused the company of overbilling patients and insurers, accusations that prompted investigations by a U.S. attorney and an informal inquiry by the SEC. It was a factor in Hanger's stock price falling from more than $18 a share in April to yesterday's close, which was the lowest level in nearly three years.

The company said Monday that an independent investigation commissioned by its board and conducted by Chicago law firm McDermott Will & Emery made a preliminary finding that the billing discrepancies were limited to the West Hempstead patient care center, which accounted for less than half a percent of sales in recent years.

In its SEC filing, the company attributed the delay in releasing earnings largely to "substantial time and efforts expended by management to cooperate with the internal investigation of certain alleged billing discrepancies."

Last year was a disappointing year for the company. Earnings fell to $16.2 million (39 cents a share) from $23.6 million (86 cents) even as revenue rose to $547.9 million from $525.5 million.