Probes into whether misuse of inside information caused extremely heavy trading activity in Carrier Corp. options in the week before United Technologies Corp. announced a takeover bid for Carrier are concentrating on large purchases made through two brokerage firms, Loeb Rhoades Hornblower & Co. and Pershing & Co.

"There was a lot of monkey business, and Pershing & Co. and Loeb Rhodes really came in and bought a lot of those calls," said one market maker on the Midwest Stock Exchange where Carrier options are exclusively traded.

But officials of both brokerage firms noted that they serve as clearing firms for large numbers of other brokers and that orders executed through them would not neccessarily represent their own customers.

Between us and Loeb Rhoades, the buying could be coming from 100 firms," said Michael Boyd, senior vice president and general council for Donaldson, Lufkin & Jenrette Securities Corp. Pershing & Co. is a wholly owned division of Donaldson Lufkin that specializes in clearing.

Boyd said Pershing had received a letter from the Midwest Stock Exchange dated Oct. 19 requesting names and addresses of all customers who execised 10 or more contracts in the Carrier September series from Sept. 11 through Sept. 16, the number of contracts in customer accounts that went unexercised, the number of calls exercised through the firm's proprietary account and a large number of other specific pieces of information relating to the trading.

"We have not accumulated any of this information yet," said Boyd.

A Loeb Rhoades spokeswoman noted that the firm provides clearing functions "for at least 65 other firms."

Both the Midwest Stock Exchange and the SEC are known to be investigating the unusual trading activity in Carrier options following complaints by market makers, several of whom were forced out of business when Carrier stock and its related options shot up in price following United's $28-a-share tender that was announced on Sept. 18.

"There have been enough questions raised by the volume of trading that week to warrant an inquiry . . . and that inquiry is in process," said Kenneth Rosenbloom, general counsel for the Midwest exchange.

The SEC has been concerned about an apparent pattern of advance leaks prior to announced tender offers that have sent the shares of many target companies climbing before the bids are made public.

"There are several cases involving information in advance of deals that should be coming out within the next month," said Theodore Levine, associate director of the SEC's enforcement division. He said the SEC has tried to increase its surveillance in this area, is working more closely with the exchanges and also is considering whether new rules may be needed.

In the case of Carrier, the focus is not so much on buying of shares - though this also may have been involved - as on purchases of call options.

These options significantly leverage, or multiply, the advantage an investor with advance information may have, while limiting the price impact on the underlying stock which would result from heavy direct purchases.

Carrier's stock went from $20 a share to $26.75 after the United Technologies announcement for an increase of 33 percent. Carrier's December and March options, however, traced increases of between 250 percent and 475 percent.

The potential for the Carrier $20 options which expired on Sept. 15 was even more staggering. These options could have been purchased that week for as little as $6.25 for 100 Carrier shares. If the options were exercises on the expiration date - which was three days before the tender offer was announced - this $6.25 investment would translate into a profit of $675 when profits were taken on the stock, for a 10,800 percent gain.

"There was nothing unusual in the trading of the call options in that period when you look at the volume of the underlying stock," said the Midwest Exchange's general counsel Rosenbloom in explaining why the exchange did not intervene in the trading.