IT'S A SIGN OF THE TIMES. The old-line New York firm of Whitman & Ransom has taken on its first specialist in criminal law - John McQuire Dowd, former head of the Justice Department's Organized Crime Strike Force - as a partner in its Washington office so it can capture a share of the growing business defending businessmen and politicians accused of white collar crimes.

Moreover, the Fifth Avenue firm is looking for another criminal law partner for its New York office - something no repubable firm specializing in corporate law would have thought of doing a few years ago.

"It's new for them," said Dowd, who had been with Justice since 1969. "They want to be full service law firm."

Being a full service law firm these days means being able to handle criminal cases. " A major New York law firm wouldn't touch a criminial case with a 10-foof pole in the past, but now they are being forced to when chairmen of the boards are being indicted," said one Washington lawyer.

Dowd said he is spending his time with Whitman & Ransom "doing what I spent my time in government doing" - only this time he's on the defense, not the prosecutor's side. He said he already has lined up a number of clients, but declined to name them.

Dowd built up a reputation in the Justice Department as a hard-nosed prosecutor of organized crime. He was involved in the investigations that led to the recent indictments of two Pennsylvania congressmen, Daniel Flood and Joshua Eilberg, both Democrats, and last March he was being considered for the still unfilled post of U.S. attorney for the eastern district of Virginia.

He is the second well-known Justice Department white collar crimes prosecutor to cross the street to become a defense attorney. Barnet Sckolnik, the assistant U.S. attorney in Baltimore who prosecuted Vice President Spiro T. Agnew and Gov. Marvin Mandel, announced earlier this month he was going into private practice.

They are entering a growth specialty for lawyers. The FBI and Justice Department have vastly increased their attack on white collar crimes, including political and corporate corruption. In the past six years, for instance, there has been a more than 500 percent increase in federal prosecution of state and local officials and the FBI reports that convictions on white collar crimes have doubled since 1972.

Defending corporate executives accused of white collar crimes can also be highly lucrative. According to the National Law Journal, fees for a typical case run to $50,000 while major cases cost more than $1 million.

"White collar crime is very much in vogue these days," said one Washington lawyer, "and firms like Whitman & Ransom do not see why they shouldn't handle it themselves instead of referring it to specialists in other firms."

Former Securities and Exchange Commission Chairman Roderick M. Hills is back in the private practice with his wife, Carla A. Hills, a former secretary of Housing and Urban Development.

The two are partners in the Washington office of Latham, Watkins & Hills, a Los Angeles firm whose west coast name is Latham & Watkins. Carla Hills opened its Washington office in February while ROderick Hills was working - in a job he now calls "a mistake" - as president of Peabody Coal Co.

The Hillses had been partners in another Los Angeles firm - Munger, Tolles, Hills & Rickershauser, which they started in 1962 - before coming to Washington to join the Ford adminstration.

Hills said he will be doing what he always did - handle negotiations in labor disputes, investment banking and corporate law.