The Securities & Exchange Commission and the New York Stock Exchange are investigating stock trading prior to the Blackstone Group’s $26 billion acquisition of Hilton Hotels Corp., sources tell me.

The Blackstone-Hilton transaction was officially announced the evening of July 3. Prior to the disclosure, Hilton’s stock jumped 6.4%, to $36.05, on increased trading volume. That action raised eyebrows among some regulators, suggesting that some investors may have had advanced knowledge of the deal and illegally traded on it.

In recent weeks, I’ve learned, the SEC and the Big Board have sent inquiries to brokerages seeking names of clients both in America and abroad who traded in Hilton’s securities. In the SEC’S case, its focus is on trading that occurred on Hilton stock between April 2 and June 15. The NYSE is zeroing in on trading that took place on July 2.

Anyone who bought Hilton shares on July 3 made a killing. On July 5, the first day of trading after the July 4 holiday, Hilton jumped 26%, to $45.51.

The probe is the latest in a growing number of regulatory investigations into giant-size mergers, acquisitions and leveraged buyouts. In numerous instances, the shares and options of target companies have risen suspiciously in advance of public announcements, suggesting to some regulators that illegal trading on inside information is once again running rampant on Wall Street, as it did during the M&A heydays of the 1980s.

“It’s the Wild West of Wall Street all over again,” a brokerage compliance official with strong regulatory contacts told me. “It’s like who can rob the next bank first.” Spokesmen at both the SEC and the NYSE declined to comment on their Hilton probes, but a regulatory contact familiar with the investigations confirmed them to me.

Speaking of investigations, the SEC is also probing stock trading in Advanced Micro Devices and ATI Technologies, while the NYSE is doing likewise with AVAYA Inc. Within the past two weeks, trading information on all three companies was solicited from the brokerage community.

In another regulatory development, a hedge fund trader who agreed to speak to me on condition of anonymity acknowledged he had been contacted by the SEC with regard to two trades he had made on stocks prior to their both being mentioned on CNBC. He told me he made about $82,000 on the two trades. He also said he informed the SEC in a lengthy phone conversation that he had discussed the stocks with “a friend” at the network before trading in them, but he insisted he had no clear knowledge they would be mentioned in a TV report. He declined to tell me the name of his friend.

An SEC spokesman said he wouldn’t comment on the matter. CNBC officials could not be reached for comment by press time.

Meanwhile, the SEC is moving ahead with its reported investigation into the trading of Dow Jones stock prior to the May 1 disclosure that Rupert Murdoch’s News Corp. had proposed a $5 billion, or $60 a share, offer for the publishing firm.

The SEC’s investigation into the trading in Dow Jones securities extends about two months beyond the May 1 public disclosure date. This suggests that the agency may be interested in determining who had access to certain relevant matters involving the company following the announcement of Mr. Murdoch’s bid, and whether they traded on that non-public information.

On July 12, I’m told, the commission fired off a request to brokerages for the names of clients who traded in Dow Jones securities between March 19 and June 30 in both domestic and overseas markets.

dandordan@aol.com