WASHINGTON (AP) _ The NAACP Legal Defense and Educational Fund Inc., re-evaluating civil rights strategies for the rest of this decade, has concluded that top priority must be given to ''the urgent plight of underclass blacks.''

A fund committee, concluding a 14-month assessment of where the civil rights movement stands, found that 31 years after the landmark Supreme Court decision outlawing separate-but-equal treatment for races, millions of blacks remain poor, under-employed and under-educated.

It also blamed the Reagan administration for creating a climate which ''is almost universally perceived to be unfavorable to the advancement of civil rights law and to meeting urgent needs of blacks.''

It chided the Justice Department for ''actively campaigning to reverse gains made in the laws especially with regard to affirmative action and school desegregation.''

The department ''will undoubtedly move even more vigorously and confidently under its interpretation of the 1984 election results,'' in which President Reagan, with only minuscule support from blacks, rolled to a landslide victory over Democratic candidate Walter F. Mondale, it said.

Attorney General Edwin Meese III has said he is proud of his department's civil rights enforcement record. But at the same time, Meese, and civil rights chief William Bradford Reynolds have tried to roll back race-conscious, preferential hiring and promotion programs, saying they discriminate against people who don't benefit from such programs.

The study was commissioned by Julius Chambers in June 1984, shortly after he became the new director-counsel of the New York-based civil rights lawyers' organization. The committee was asked to review NAACP Legal Defense and Educational Fund programs to determine if they were meeting the needs of blacks.

What the panel concluded was that civil rights lawyers must plan and implement new strategies ''to attack the exclusion of black Americans from full and equal participation in this country's educational, economic and political processes,'' the report said.

A commitment to ensuring equal opportunity for undereducated and untrained blacks was one of the panel's key recommendations. It said this goal ''should be pursued with the same creative fervor that overturned the 'separate-but- equal' doctrine'' in the landmark decision involving Brown vs. the Board of Education in 1954.

Just as that decision ''was the culmination of a well-coordinated strategy developed over 20 years, the committee proposes that LDF develop an action plan to refocus some of the existing budget resources and create new legal strategies that will link LDF's new focus with the overall struggle for civil rights,'' the report said.

It noted that according to the Census Bureau, 1983 saw the highest black poverty rate since 1968, with 9.9 million, or 35.7 percent, of the black Americans categorized as poor.

Last Friday, the Labor Department's unemployment report for September showed that joblessness among black adults jumped signficantly, from 14 percent to 15.3 percent, more than twice the 6.1 percent rate of white adults.

''For millions of Americans, the promise of Brown remains unfulfilled,'' the report said. ''Over 30 years after the landmark Supreme Court decision which put an end to legally enforced racial segregation, the plight of blacks as a whole has worsened - and there is alarming evidence that they are becoming a permanent underclass.''

Pointing to new directions in the 45-year history of the legal defense organization, the committee called for ''multiple strategies, such as legislative remedies, coalition-building and public education,'' to improve the opportunities of young blacks.

''With the greatest threat now coming from the federal government,'' it said, ''the traditional adversaries (of civil rights advancement) might be looked to as new allies.''

The report suggested greater collaboration in civil rights efforts with groups representing Hispanics, because of ''the concentration of blacks in geographic areas with Hispanics and other minorities.''