President Reagan nominated two prosecutors from the U.S. attorney's office yesterday to fill vacancies on the D.C. Superior Court, bringing to 26 the number of local judges he has named -- more than half of the court's members.

The nominations of Harold Cushenberry and Michael Rankin, both of whom are black, bring to seven the black men Reagan has named to the local court since taking office in 1981. He also has nominated one Hispanic and five women, one of whom is black.

Yesterday, several court observers, noting that half of his appointees have been minorities or women, said the record is impressive. The court has 51 judges, of whom 16 are black.

"It is almost a third in terms of blacks and 20 percent in terms of women," said Frederick B. Abramson, president of the District of Columbia Bar and former chairman of the D.C. Judicial Nomination Commission. "It is a very impressive record, helped by these last two nominations . . . . I did not expect it to be this good, but I am pleasantly surprised."

Cushenberry, 35, is currently the executive assistant to U.S. Attorney Joseph E. diGenova, and previously has worked in various divisions of the office. He spent two years handling the prosecution of major felony cases, and was deputy director of the office's operation in Superior Court. A Harvard graduate, he joined the office in 1977, two years after completing law school at Georgetown University.

Rankin, 39, currently deputy chief of the felony trial division in the prosecutor's office, also has experience as a criminal defense lawyer. He worked for four years for the D.C. Public Defender Service, which represents indigent defendants in criminal cases, and later served as the acting federal public defender in the Virgin Islands. A graduate of Lincoln University in Missouri, he attended law school at Howard University. He joined the U.S. attorney's office in 1980.

Cushenberry and Rankin were nominated to fill vacancies created on the bench when the terms of Judges Nicholas S. Nunzio and Paul F. McArdle expired.

Yesterday, Abramson compared Reagan's record of nominations with that of President Jimmy Carter, who named 15 judges to the local bench, including five black men and four women, two of whom are also black. "Carter did slightly better, but that is not to dispute that the Reagan record is very good," said Abramson.

For each vacancy, the seven-member Judicial Nomination Commission sends three names to the White House, and Reagan chooses one as a nominee. That person must then be confirmed by the U.S. Senate.

In the vast majority of cases, the nominating lists were balanced, including at least one white male, according to court sources. "So the White House has never been forced to appoint a minority or a woman," one source said.

Others noted the quality of the nominees. "One thing is for sure, that the president has consistently chosen people for the bench of high quality, judicial temperament and integrity," said diGenova, also a Reagan appointee. "The Superior Court bench is as good as any in the country now."

John A. Turner Jr., president of the predominantly black Washington Bar Association, said he was "very much encouraged" by the Reagan record."There had been a need and still remains a need to increase the total number of black judges on the bench so the percentages are more in keeping with the population of the city," Turner said. "There is progress in that direction."

Patricia N. Gillman, president of the Women's Bar Association, said, "We can never complain when women are nominated. It's a step in the right direction . . . . But we want more, and we have a lot of extremely qualified members."