bandages and ADT security systems, fell sharply yesterday after the Bermuda-based conglomerate said the Securities and Exchange Commission was looking into its accounting practices.

Tyco, dogged for months by questions about the way it has accounted for its aggressive buying spree, said the SEC has launched an informal inquiry into charges and reserves taken in connection with the purchases.

Tyco shares slid in very heavy trading, dropping 8-9/16 to 27-5/8, off a record close of 53 in October. Tyco was the most active issue on the New York Stock Exchange, with more than 57 million shared traded.

Typically, the SEC starts an informal inquiry if it believes there is information that needs to be investigated. An informal probe can expand to a formal investigation, which can lead to the filing of civil or criminal charges.

Tyco, which is based in Bermuda but managed from Exeter, New Hampshire, said the SEC had told it on Wednesday of the probe. Tyco added that it was cooperating with the investigation.

"We remain confident of our accounting methodology, our public disclosures and the continuing strength of our business,'' said Chairman and Chief Executive L. Dennis Koslowski.

Tyco's shares have fallen from a 12-month high of 53 on October 11, shortly before Dallas research firm David W. Tice raised questions about its accounting practices.

Some of the criticism has stemmed from Tyco's use of pooling-of-interest accounting for some of its purchases.

In at least two instances, companies being bought by Tyco slowed their revenue growth or wrote off significant assets in the final quarter before being bought.

This enabled Tyco to show greater earnings growth in later periods than it would have otherwise.

Tyco is one of the most aggressive buyers in the United States of other companies. It has announced 39 purchases since the start of 1998, and 18 this year, according to Thomson Financial Securities Data Corp.

Its businesses range from the world's biggest fire and security business, including security monitoring company ADT, to underwater fiber cables, Curity bandages and steel pipe. Its 1998 revenues totalled $12.3 billion.

Problems: Tyco International CEO Dennis Kozlowski pictured in Essex, New Hampshire in June, watched shares in his company plunge more than 23 percent yesterday after the SEC started probing its accounting practices.