Chief Judge Harold H. Greene of the D.C. Superior Court, who guided the city's court system through its early, delicate years of long-needed reforms and new independence, was nominated by President Carter yesterday to a seat on the U.S. District Court here.

The nomination, if confirmed by the Senate, marks the end of Greene's 12-year tenure as a judge of the local court, during which time he earned the reputation of a legal scholar while he directed the transformation of the old, problem-plagued Court of General Sessions into the larger, more powerful Superior Court.

"It has been my life for 12 years, Greene, 55, said in a telephone interview. The chief judge, who is vacationing in South Carolina, learned of the long-expected nomination from one of his law clerks yesterday afternoon.

As chif judge, the principal administrator of the court, Greene quietly shepherded the system through its years of reorganization, instituting reforms to eliminate much oif the chaos and delay that had come to characterize the Court of General Sessions.

Knowledgeable sources mentioned some of the current Superior Court judges as likely candidates for the chief judgeship should Greene move to the federal court. Among those mentioned are James A. Belson and John Garrett Penn, both of whom frequently handle civil cases, and H. Carl Moultrie I, who regularly presides over serious criminal trials.

Named an associate judge of the General Sessions Court in 1965, Greene was once described as a "maverick" who worked long hours, through his courtroom and was intolerant of the conduct of some attorneys who roamed the courthouse looking for clients.

Fourteen months after he joined that court, Greene was named its chief judge. Through simple changes, such as renovation of the court buildings, caldendaring procedures to cut delays, and computerized record keeping, the local courts took on new appearance of efficiency and dignity.

As a judge whose written opinions are known for their clear and careful analysia, Greene secured for indigent torneys. He laid the legal groundwork for the right to demonstrate at the Capitol, and ordered the city to overhaul its methods for detaining juvenile offenders.

Greene said yesterday that he is "eager" now to move on the federal bench, although he said he has some "mixed emotions" about his departure from the Superior Court.

"I'm ready to leave in the sense that court reorganization is over the the (new courthouse) building is finished," Greene said. "Those were the two overriding projects I was associated with so it seems like a good time to go on to a new challenge," he said.

The new District of Columbia Courthouse, a $40 million glass and stone building on Indiana Avenue NW, is in some ways the product of another of Greene's roles as chief judge of the Superior Court - that of chief lobbyist and "legal politician" for the city court system.

It was only after protracted negotiations and much testimony from Greene that Congress in 1974 appropriated the money for construction of the courthouse, which is expected to be dedicated within the next two months!>.

In recent years, in his role as administrator of the court, Greene has faced criticism from some lawyers and courthouse administrators who say that he has become too tighfisted with his authority, is unwilling to delegate decision-making power and thus cuts into the efficient operation of the Superior Court.

Currently housed in seven buildings, the Superior Court has a total of visions of the court that become tangled in case backlogs has also been a point of dispute among court watchers.

In 1971 the Court of General Sessions, a much maligned "police court" that handled petty offenses and minor civil cases, was merged into the new D.C. Superior Court, which had broader general jurisdiction over a wide range of offenses.

Eventually, the Superior Court assumed jurisdiction over all local criminal and civil cases, once handled in the U.S. District Court. The Superior Court also has jurisdiction over local probate matters, such as wills, both civil and criminal tax cases under District law, domestic relations and juvenile cases.

President Carter selected Greene to fill a vacancy on the federal bench that opened when U.S. District Court Judge John J. Sirica stepped down form his full-time duties last fall and assumed senior Judge status. That 15 member federal trial bench has another vacancy that resulted when Judge Howard F. Corcoran also took senior status last fall.

If Greene's nomination is approved by the Senate, a new chief judges, a lawyer who is not a judge could be named to the post, according to Charles Duncan, a professor ar Howard Law School, who is chairman of the commission.

The chief judge serves for a term of four years.