Stock trading investigations are on a brisk pace in 2007, running between about 10% and 12% ahead of last year’s levels through the end of March, regulatory sources tell me. These figures cover probes by the Securities & Exchange Commission and the various stock exchanges.

Major corporate names are included among some of the more recently initiated trading investigations. They include studentloan giant SLM Corp., better known as Sallie Mae; Royal Caribbean Cruise Ltd., the world’s second-largest cruise line, and AMR Corp., parent of American Airlines, the country’s largest carrier, a regulatory source said.

An SEC spokesman, John Heine, would say only: “We neither confirm nor deny investigations.”

The SEC probe, which the source said covers trading in Sallie Mae shares during about a threemonth period between November 6 and February 6, comes on the heels of recent disclosures of government investigations into the $85 billion student loan market, which has led to selling pressure on Sallie Mae’s shares.

Late last month, for example, the chairman of the House Committee on Education and Labor, Rep. George Miller, a Democrat of California, sent letters to the nation’s five largest loan providers, including Sallie Mae, requesting information about their relationships with college financial aid offices. In his letter, Mr. Miller cited “significant concerns” regarding student loan providers offering gifts or other “questionable incentives” to colleges that agree to encourage students to take out their loans with specific lenders.

The four others that received letters from the committee were Citibank/The Student Loan Corp., Bank of America, Wells Fargo Corp., and JP Morgan Chase & Co.

Last November, the attorney general’s office also began an investigation into the practices of student loan providers and requested information from Sallie Mae, among others.

The SEC already has sent out questionnaires to the brokerage community in which it requested the names of all clients, both in America and abroad, as well as in-house personnel, who traded in the stock in the specified time period.

A Sallie Mae spokesman said: “We’re not going to comment on that, and that doesn’t mean we’re confirming we have any knowledge of what you’re asking us about.”

Worries about investigations into the student loan business have clearly taken their toll on Sallie Mae’s shares, with the stock skidding to a $48.77 close last year from a high of $58.35. This year has seen a continuation of the declining trend, with the stock falling another 16% to its current price of $40.90.

Despite the drop, plenty of investors seem to think the flow of bad tidings is far from over. One indicator is the latest figures showing Sallie Mae still sports a hefty short interest (a bet the stock price will fall) of 6.7 million shares, though that’s down from 8.8 million shares the prior month.

Speaking of stock trading investigations, sources tell me the SEC is also conducting similar probes involving the following companies:

• 3Com Corp., which sells networking hardware and software.

• Lexicon Genetics, which is engaged in pharmaceutical research and uses mice with a particular gene function to study the potential effects of drugs on various genetic targets.

• Petrohawk Energy Corp., (formerly Betta Oil and Gas), an oil and gas exploration and development company.

• And Lodgian, a multi-brand franchisee of some 70 hotels in nearly 30 states and Canada.

The National Association of Securities Dealers, sources tell me, has also begun four new trading investigations, two of which are in the health care industry. One involves Halozyme Therapeutics, a maker of enzymes for infertility, cancer, and eye surgery applications. The other is Acorda Therapeutics, a developer of therapeutics designed to restore neurological function for patients with spinal cord injury and other central nervous system disorders.

The other two Nasdaq investigations center on Cree, a maker of semiconductor material devices, and Rackable Systems, a provider of rack-mounted servers designed for large-scale data center deployments.

Asked about the four investigations, a Nasdaq spokesman declined comment.

In yet another development on the regulatory front, talk in investigatory circles has it that the SEC is about to involve itself, if it hasn’t already done so, in an investigation of Beazer Homes. The FBI has already announced that it’s investigating the homebuilder on allegations of mortgage fraud and other possible wrongdoings.

The SEC declined comment, and Beazer did not respond to several calls seeking comment.

dandordan@aol.com