By Svea Herbst-Bayliss

NEW YORK (Reuters) - Billionaire investor Bill Ackman's plans to turn real estate company Howard Hughes Holdings into a diversified holding company will not impact how his investment portfolios buy and sell stakes in companies.

Ackman's flagship Pershing Square Holdings portfolio will continue to buy large stakes in large companies while Howard Hughes will buy controlling stakes in small companies, he explained on a conference call.

"These are two different worlds," he added, noting it is possible to pursue both types of investment strategies.

The investor who began his professional life as a corporate activist by pushing companies like railway Canadian Pacific to perform better is now reshaping his hedge fund firm, Pershing Square Capital Management, into a diversified financial group.

After retiring from his "vocal" corporate agitator life three years ago, Ackman has spent the bulk of his time creating what he calls "modern-day version of Berkshire Hathaway."

Under a revised proposal for Howard Hughes, Ackman would offer $900 million and increase his stake to 48% from 37.6%.

He would also become the company's CEO after having been involved with the company for more than a decade and having served as its chairman until he stepped off the board early last year.

On a conference call on X, Ackman said the new Howard Hughes would offer a permanent home to small businesses that it likes. "You will be important to us," he said, adding that he wouldn't buy the interests only to sell them again in a few years.

Nearly a year ago Ackman laid the groundwork for a new fund designed to let U.S.-based investors tap into the kind of double-digit returns his Pershing Square Holdings fund has been delivering for years.

He scrapped the launch of Pershing Square USA only days before it was slated to begin trading on the New York Stock Exchange after he shrank the fundraising target to $2 billion from $25 billion.

Ackman has said privately that he will try again for an initial public offering for the fund and has met with bankers to gauge interest but that his first priority is finalizing the Howard Hughes deal.

(Reporting by Svea Herbst-Bayliss; Editing by Chizu Nomiyama)