A lawyer who avoided paying income taxes for almost 25 years will spend 45 days in jail and pay $1.5 million after pleading guilty to failing to file tax returns, prosecutors said Monday.

Francis K. Decker Jr., who specialized in defending tobacco companies, pleaded guilty Friday, admitting he failed to file personal state and city tax returns since 1998 on $4.5 million in gross income, prosecutors said.

Because Decker, 70, was a partner at a Manhattan law firm, no taxes were withheld from his pay, and he made no quarterly estimated income tax payments as required by law, prosecutors said. However, they said, he signed statements telling the firm he had filed returns and paid his taxes.

Manhattan District Attorney Robert Morgenthau said Decker, who has homes in Brooklyn and Quogue worth $2 million each, was caught when state officials did a routine review of license databases and found he was a licensed lawyer in New York but was not paying taxes.

A condition of Decker's plea deal is that he must settle with federal tax officials, if necessary, said Assistant District Attorney Daniel Castleman.

Morgenthau said Decker had not filed tax returns since 1982. He said it was ironic that a person who paid no income taxes for decades could avoid detection more easily than someone who occasionally paid but sometimes cheated.

The statute of limitations did not cover income tax offenses before 1999, but Decker agreed to pay going back to 1982.

Besides spending 45 days in jail, Decker will pay a $10,000 fine on each of two counts of failure to file, prosecutors said. He also must pay $779,757 in state and city personal income taxes, interest and penalties for 1999 through 2005 and $720,000 to settle any tax liability for 1982 though 1998. He will be sentenced Feb. 1.

Decker's lawyer, Jonathan Davidoff, said his client "has accepted responsibility for his actions and is very sorry for his past behavior."

"By accepting responsibility," Davidoff said, "Mr. Decker has not only agreed to pay New York state back for past taxes but also is paying society back by pleading guilty and serving the sentence recommended by the district attorney's office."