A far-reaching affirmative action agreement, seeking to guarantee more federal jobs for blacks and Hispanics, was accepted with some changes by the Reagan administration yesterday in papers filed here with U.S. District Court Judge Joyce Hens Green.

The agreement, arising from a lawsuit charging that the federal Professional and Administrative Career Examination blocks blacks and Hispanics from getting jobs, was first negotiated by the Carter administration and signed by the Justice Department and the plaintiffs Jan. 9, only a few days before the Reagan administration took office.

There had been speculation that the administration would seek to junk the agreement or back off from the affirmative action positions it emodied, but it did not.

Attorney General William French Smith said yesterday that in view of the legal difficulty of withdrawing the consent decree, he was agreeing to it with several changes that lawyers for the plaintiffs had endorsed.

Sources said the Justice Department probably would have sought more far-reaching changes had it been free to withdraw the agreement unilaterally.

Barry Goldstein of the NAACP Legal Defense Fund, an attorney for the plaintiffs, called the agreement "a very positive statement of the national commitment to equal employment opportunity."

Office of Personnel Management (OPM) general counsel Margery Waxman said, "The new settlement is far easier for government managers to live under than the Jan. 9 version."

The proposed decree had been criticized by a number of personnel experts and by the Anti-Defamation League as akin to a quota system in which merit is subordinated, a charge denied by civil rights groups.

Under the agreement, the government over the next three years will phase out the PACE exam, since it was found that about 40 percent of the whites taking it usually pass, while the rate drops to only 5 percent for blacks and 13 percent for Hispanics. The PACE exam has been used to fill many of the best entry-level career jobs at Grades 5 and 7 in about 118 job categories.

In its place, the OPM or individual agencies will construct new tests specifically designed for the qualifications needed for each diferent set of jobs.

If the new tests fail to show a much higher percentage of blacks and Hispanics passing and getting jobs -- roughly proportional to the number who took the tests -- the exams would be subject to further legal challenges and requests that they be discarded and new tests devised.

The government, however, could escape the requirement to keep revising exams indefinitely by "validating" the just agreed to tests -- that is, demonstrating that the tests are excellent predicters of job performance.

While developing new tests, the government would have to make special efforts to recruit black and Hispanic employes, sometimes on the basis of their academic record and without a test. Such efforts would have to continue for three to five years after the consent decree goes into effect, provided the judge approves it.

Language was added to the agreement making it clear that the government has the right to modify the Uniform Guidelines, the rules that govern adminstrative proceedings in employment complaints. Sources said this will probably lead to proposals for modifications to make it easier for the government to prove the validity of a test than it is now.

The consent decree submitted yesterday to Green, who took it under advisement, would make a number of changes from the earlier version. Under the earlier version, special hiring procedures could have been mandatory for up to nine years, or until 20 percent of the work force in any category was black and Hispanic. Both the nine-year and 20 percent provisions were dropped.