Sid Davidoff's law firm is the Boston Celtics of New York City politics. It may be struggling just now, but it's remembered for one of the longest winning streaks in municipal annals, when the former aide to Mayor John Lindsay, buddy of Queens Borough President Donald Manes, and tennis partner of Mayor David Dinkins could procure a contract, license, zoning variance, or permit with a phone call.

In 1990, Mr. Davidoff explained his long reign as the city's top lobbyist to Newsday this way: "The government doesn't change that much when the top of government moves.... The government still is the same basic set of rules."

That's a proposition Rudolph W. Giuliani disputed when he set out to become Mayor. He lambasted David Dinkins, and rightly so, for his tennis dates with Mr. Davidoff. When Mr. Davidoff paid for First Deputy Mayor Norman Steisel's Miami vacation, Rudy didn't accept the explanation that the two were close personal friends who didn't talk shop when they socialized together.

More recently, however, the Mayor has denounced news stories about the lobbying of Riverdalian Raymond Harding and former Riverdalian Herman Badillo, who, The Times reported, "have built a prosperous lobbying business at their law firm even as they continue to serve as close advisers to Mr. Giuliani."

Five years ago, the same paper reported that "One of every three dollars in new lobbying money was paid to the law firm . . . headed by Sid Davidoff," whom it described as "tennis partner, friend and sometime adviser to Mr. Dinkins."

Not only doesn't the government change, even the excuses remain the same.

In 1991, Mr. Dinkins said Mr. Davidoff had never lobbied him personally. "All matters are considered on the merits," he asserted. Last week, Deputy Mayor Fran Reiter, Mr. Harding's Liberal Party protege, said she did not talk to her mentor about matters involving clients, and a testy Mayor Giuliani insisted that people who hire lobbyists "do not get an edge."

No one who has observed how government works will believe that, any more than they will believe that because Mr. Harding and Mr. Badillo have now said they will no longer personally lobby for clients, the law firm of Fishbein Badillo Wagner Harding no longer has an inside track at City Hall.

Those who lobby the executive branch are paid for knowing whom to call and knowing their calls will be returned. They are paid for gaining a respectful hearing from commissioners, deputy commissioners, and staff members who decide how contracts and requests for proposals shall be worded, and who are responsible for creating or unlocking administrative log jams.

"The people who are my advisers are following the law, the letter and spirit, in every respect," the Mayor pronounced last week. He did not accept that reasoning in the Koch or Dinkins years.

Although the City Conflict of Interest Board cleared Mr. Steisel of wrongdoing, Mr. Giuliani made Mr. Davidoff a campaign issue.

In a pivotal moment in his cross-examination of Bronx Democratic leader Stanley Friedman, United States Attorney Giuliani asked about a phone call Mr. Friedman made to facilitate a city lease. You got paid $10,000 for making a couple of phone calls, didn't you, the prosecutor asked. "It was just one phone call," the boastful Friedman replied. The answer was his undoing. Although there was nothing illegal about the call, his defiant cockiness showed the jury the seamy underside of New York City government, where access is often indistinguishable from sleaze.

In those days Rudolph Giuliani understood that what you had a right to do wasn't identical to what was right to do.

Now, however, he has developed what might be called the Mayor's blindspot--an affliction that prevents the occupants of City Hall from seeing ethical lapses.

But what the eye can't see, the nose should still be able to detect. When a political associate trades on his personal relationship to those in power to enrich himself, that smells.

Mayor Giuliani has only to think back to his triumphs in the courtroom to recognize the odor.