The Reagan administration's record on civil rights again came under attack as William Bradford Reynolds, assistant U.S. attorney general for civil rights, defended it today before a convention of skeptical black attorneys.

As Reynolds prepared to address the annual meeting of the National Bar Association, about 30 delegates walked out.

Reynolds told those who stayed, some of whom snickered and laughed at parts of his speech, how "vigorous and uncompromising" the Reagan Justice Department has been in its "war" against discrimination.

He reeled off a list of suits the department has filed in the areas of voting rights, fair housing, affirmative action and school desegregation.

"Standing alone, these facts forcefully refute the charge that the Reagan Justice Department is not enforcing civil rights, and for the most part outshines that of any previous administration."

But the delegates, who were allowed to question Reynolds after his speech, attacked his statistics and questioned his conclusions.

Colin Moore, a private attorney in New York City, said, "Statistics mean what you want them to mean, nothing more and nothing less."

Moore said the Reagan administration has opposed school busing, favored tax-exempt status for private schools that discriminate and opposed setting goals for affirmative action.

"Since you have disavowed the traditional tools, how in heaven's name do you intend to effectively desegregate this society?" he asked.

Laura Blackburne, also a New York attorney, told Reynolds that under President Reagan's Justice Department, blacks have suffered the "greatest injustice . . . since slavery." Reynolds reminded the audience that he sent 322 federal observers to Mississippi to monitor the voting there last week.

He said the Justice Department has four desegregation suits authorized for filing by the administration, has negotiated desegregation consent decrees in 15 school cases and has 14 others being litigated.

He said the administration has authorized filing complaints in nine housing discrimination cases and that his Civil Rights Division is involved in more than 100 employment discrimination lawsuits, a fifth of which, he added, were filed by the Reagan administration.

He said that under the Reagan administration his unit has brought 114 new civil rights prosecutions, 80 of which have been tried. And he said that his division filed more criminal civil rights cases last year than in any previous year. "That, my friends, is law enforcement, and it's law enforcement at a level of activity that outdistances prior administrations," Reynolds said.

However, Reynolds reminded the lawyers that the Justice Department "is not a special-interest law firm."

"We cannot tailor either our legal interpretations or our enforcement policies to serve a particular group, whether its membership is defined by economic circumstance, political affiliation, race, sex or any other similarly legally irrelevant criteria," he said.

Reynolds also defended the administration's stand against reverse discrimination.