William Bradford Reynolds, the assistant attorney general for civil rights, has set forth the yardstick by which he measures the success of affirmative action: the "number of persons who are recruited to apply" for jobs at companies with records of hiring discrimination, not the number of women or minorities actually hired.

Reynolds' definition of affirmative action came in a letter to Sen. Edward M. Kennedy (D-Mass.). He had earlier told Kennedy that instead of setting goals, timetables or quotas, the Reagan administration has had equal success in remedying hiring discrimination by requiring companies to aggressively seek job applications from qualified women and minorities. Kennedy asked for data to support that claim.

But in the 26 cases cited by Reynolds, fewer than half of the companies could provide data to show that their efforts were as effective as goals, quotas or timetables would have been in the hiring of minorities and women.

The administration is embroiled in debate over what form its affirmative action policies should take. Labor Secretary William E. Brock has said he favors goals and timetables; Reynolds has remained opposed to any affirmative action except the recruiting of applicants.

Reynolds sent his letter to Kennedy at the start of hearings in June over his nomination to the number-three job at the Justice Department. The subject of quotas, however, was not debated at the hearings, which ended with Reynolds' being rejected. Kennedy has had no comment on the letter.

Reynolds wrote that, of 26 consent decrees in which the Justice Department has used the recruitment requirement instead of quotas, goals and timetables, nine companies have either "met or come very close to meeting" the number of women or minorities that courts would have set for the companies.

But in nine other cases, Reynolds said, the companies have not hired women or minorities "in numbers approaching the estimated availability" of women and blacks in the local work force.

Of the eight remaining cases, Reynolds said that seven companies had not reported how many women and blacks had been hired and the other firm had not hired anyone since the consent decree took effect.

Reynolds said the recruitment measure the administration supports for offsetting proven hiring discrimination is not necessarily the number of women or minorities hired.

"Where enhanced recruitment is required," he wrote, "success is measured first in the number of persons who are recruited to apply . . . the purpose of an enhanced recruitment requirement is to correct the current effect that prior discrimination has in discouraging potential minority or female employes even from applying.

"Once this discouraging effect is overcome," he continued, "then the required nondiscriminatory selection procedures ensure that all are treated equally. Hiring figures are relevant only as a means to monitor the nondiscriminatory nature of the hiring process."

Reynolds noted that seven of the nine cases in which hiring rates fell short of levels that courts might have imposed involved recuitment of women by law enforcement agencies and may reflect a lack of interest in those jobs among women.

Yesterday, Clarence Thomas, chairman of the Equal Employment Opportunity Commission, said the agency plans to abolish the use of quotas as a remedy for hiring discrimination by implementing major changes in the Uniform Guidelines on Employee Selection Procedure.

The rules are used by all private and public employers as a standard for avoiding hiring discrimination suits by the EEOC.

Thomas said the rules, which compare the rate of hiring and promotion for minorities and women with that for the rest of the work force, "seem to assume some inherent inferiority of blacks, Hispanics, other minorities and women.

"The use of mechanical statistical rules to define 'discrimination' encourages employers to discriminate in order to secure the work-force composition necessary to satisfy the statistical rule," Thomas said at a news conference outlining the EEOC's goals for the coming year.

He said he will seek revisions to federal employment rules that "will not require federal agencies to adopt quotas in any form . . . .