The Supreme Court’s decision to uphold the constitutionality of New York State’s official method for selecting trial judges was blind to a significant fact: In New York City, more than 40% of those judges are picked by an altogether different and unofficial process that has largely escaped scrutiny.

Last week’s unanimous decision dealt with the party conventions Democratic and Republican organizations use to nominate their candidates to run for state Supreme Court, which, despite the name, is the state’s basic trial court. Critics had complained that local political bosses controlled the party conventions.

Surprisingly, at no point in the four-year legal lead-up to last week’s decision did proponents of the conventions, their critics, or the federal judges reviewing the case so much as point out that many of the state Supreme Court justices in New York City get their jobs through a different route. They begin as lower court judges who receive promotions to the state Supreme Court from an administrative judge. That process, some lawyers say, has no basis under the state constitution, which provides guidelines for how the judges of the various courts will be selected.

This de facto appointment system, which court officials say ameliorates a chronic shortage of judges, sits in the blind spot of the ongoing debate over how New York ought best select its judges.

In New York City, 176 justices on the Supreme Court were elected, meaning they likely went through the nominating process reviewed by the U.S. Supreme Court. Another 128 were lower court judges elevated to the Supreme Court by the court bureaucracy, according to figures supplied by a court spokesman, David Bookstaver. These judges, who generally come from the city’s criminal and civil courts, are known as “acting” Supreme Court justices.

“This is a pure and unvarnished appointment system,” a lawyer who helped bring the recent challenge to the U.S. Supreme Court, Kent Yalowitz, said. “It’s a perfectly fine way to pick judges, it’s just not the one that the constitution of New York requires.”

Here’s what the state constitution says about the selection process: “the justices of the supreme court shall be chosen by the electors of the judicial district in which they are to serve.” That would suggest some level of voter participation is required, and the case before the Supreme Court focused on whether the party convention systems were unconstitutional because they stymied voter participation.

The constitution does allow the chief administrator of the courts to make “temporary assignments” to the state Supreme Court from the lower courts. In an interview, the chief administrative judge for the New York court system, Ann Pfau, cited that provision as the authority for the appointments of “acting” supreme court judges.

“It’s in the constitution,” Judge Pfau said. “It’s available as a tool.”

A court decision from 1982 by the state’s highest court gives some support to her claim.

Yet many of the appointments stretch the meaning of temporary, with “acting” Supreme Court judges routinely staying on the bench for a decade or longer without ever coming up for election. While their appointments are reviewed each year by the chief administrative judge, the decision is handled entirely by the judiciary.

“Their appointments seem less temporary as the days go by,” a lawyer at the firm Ganfer & Shore LLP, Thomas Curran, said of the process.

The reason for this secondary system for picking judges is no secret. The number of spots on the Supreme Court is capped by the state constitution to one for every 50,000 residents. That limit has led to a shortage of judges especially in Manhattan, where the number of business disputes, as well as of felony indictments, is not directly tied to the number of residents who live on the island. To get around the cap, the state court system has for at least three decades been bumping up judges from the lower courts to become “acting” Supreme Court justices.

“The question of constitutional nicety is interesting, but the fact is that New York as a commercial center and metropolitan center with a criminal docket has to function come Tuesday, when the courts re-open,” Mr. Curran said.

Other lawyers say the system is constitutional.

“I do believe that the present system — whereby the chief administrative judge has the power to appoint judges to be acting supreme court justices — is both constitutional and necessary given the situation that we face today,” the city’s corporation counsel, Michael Cardozo, said in an interview.

The New York State courts are a patchwork system under which judges routinely spend their careers hearing types of cases other than the ones they were elected or appointed to decide. Judges who are appointed by Mayor Bloomberg to the city’s criminal court are often bumped up to serve on the state Supreme Court. The same is true for those elected to a position on the city’s civil court.

The complexity of the system is reflected in Judge Pfau’s resume. Mayor Giuliani appointed her in 1998 to a 10-year term on the city’s criminal court. Yet that is not the job she currently occupies. In 2001, she was made an acting Supreme Court justice by the chief administrative judge, a position she has occupied since her appointment last year. With Judge Pfau’s original appointment to the city’s criminal court set to expire this year, she will seek reappointment to that court by Mr. Bloomberg. As the chief administrative judge, it would fall to Judge Pfau to decide whether to reappoint herself as an “acting” Supreme Court justice. She said she would recuse herself from that decision.

This patchwork system has few detractors. Some lawyers believe an appointment system leads to a smarter bench overall than an elective system. They say that many of the most competent judges started out in city’s criminal court before being promoted to “acting” Supreme Court justice. Judges who believe they lack the political connections to get elected rely on the system as an alternative way to get to the Supreme Court bench.