Thomas Patrick, executive vice chairman of Merrill Lynch & Co. Inc., retired abruptly yesterday, surprising Wall Street.

Patrick was the architect of the securities firm’s drastic cost-cutting efforts of recent years.

His departure concentrates power ever more firmly in the hands of the chief executive, Stanley O’Neal, who succeeded David Komansky in 2002.

The decision by Patrick, 60, to retire so unexpectedly comes just as the cost-cutting program he had championed was finally beginning to bear fruit.

Since 2000, Merrill has dismantled a global empire that Komansky had spent billions of dollars building.

Merrill, under O’Neal and Patrick, was the first major firm to start cutting back, laying off bankers while the bull market in technology stocks was still on its last legs.

Criticized at the time, the strategy is now widely seen as a success.

Merrill has eliminated more than 22,000 jobs in about three years and has shed businesses in Japan and Canada.