"Are there any particular fields of law you think you excel in?" lawyer Kenneth M. Robinson was asked in U.S. District Court here yesterday.

"Lots of them," he replied in a South Carolina twang. "Drugs, fraud, prostitution." When people are accused of "any of the dirty crimes, I would be the lawyer," Robinson said, "but not taxes."

Yesterday Robinson, who referred to himself as "an enemy of the government," found himself appearing for the government. The flamboyant defense attorney, whose clients have ranged from alleged international drug dealers to former South Carolina congressman John Jenrette, was a key prosecution witness as two of his former clients -- Herbert and Mary Cole -- sought to have their guilty pleas withdrawn.

The Coles, former landlords of massage parlors, topless bars and peep shows on 14th Street NW, are in federal prisons after having pleaded guilty in August to income tax evasion. Herbert Cole also pleaded guilty to racketeering charges stemming from his involvement in two massage parlors that prosecutors said were fronts for prostitution.

In their bid to set aside their sentences and convictions, the Coles charge that Robinson did not properly represent them. They said that at the time Robinson was negotiating a plea bargain for them with federal prosecutors in Washington, Robinson himself was the target of a federal tax investigation in Baltimore and did not tell them about it.

The Coles said they found out only after their sentencing that the same Internal Revenue Service agent who had investigated them had investigated Robinson.

At a hearing yesterday before U.S. District Judge Thomas A. Flannery, Robinson described his legal tangles. He said he was granted immunity on possible income tax charges last summer in return for agreeing to testify in Baltimore against another former client, Linwood Gray, whom Robinson said threatened to kill him.

Gray was convicted of concealing assets from the IRS and of conspiracy in threatening to have Robinson killed in a dispute over a house that he gave to Robinson for legal fees.

But Robinson said yesterday he told Herbert Cole about his own tax troubles and that "I felt I was being framed" by the same IRS agent. Robinson said he also told Cole about his own plea agreement shortly after he made it and said Cole "laughed and he wondered why I couldn't get him a deal like that."

In the courtroom Cole shook his head.

Earlier, Herbert and Mary Cole testified that Robinson had never told them about his tax troubles except for a brief mention that he was being audited.

Cole said that Robinson asked him for a $100,000 loan from the $5 million he would receive from the sale of the Casino Royal building on 14th Street. Cole's present attorney, Roger E. Zuckerman, said the request created a conflict of interest, but Robinson strongly denied that and added that the loan was never made. Robinson said that five other lawyers hired by the Coles also approved the plea agreement.

Herbert Cole is serving a sentence of two to eight years in prison. Mary Cole is serving a term of six months to three years. Under the plea agreement, they paid $1.5 million to the IRS.

Flannery is expected to issue a written opinion in the case shortly.