A federal court judge yesterday ordered the NAACP Legal Defense and Educational Fund, which has won many of the landmark civil rights battles of the last three decades, to drop from its name the initials of the organization that founded it 43 years ago, the NAACP.

The ruling by U.S. District Court Judge Thomas Penfield Jackson came at the request of the NAACP, the nation's oldest civil rights organization, which had contended that the use of its initials by the fund, which became independent in 1957, would cause "harmful confusion."

Jackson ruled that the fund has used the name for more than 25 years on authority of a "revocable license" granted by the parent organization in an effort to divide its legal activities from its lobbying, legislative and other types of action.

"To permit the LDF to go its own way while retaining the NAACP initials is likely to result in further public confusion," Jackson said, and ordered the fund to change its corporate charter and to stop using the NAACP name in all ways.

William T. Coleman, chairman of the fund's board, said the order would be appealed. "It's our name, too," he said.

"Obviously," Coleman said, "with all the problems involved in the civil rights movement . . . I just think it's a tragedy that we are spending our time fighting over a name rather than fighting the enemy."

NAACP executive director Benjamin L. Hooks called it a "landmark decision."

"This is a victory which we celebrate with some sadness," said NAACP board Chairman Margaret Bush Wilson, "because we were most reluctant to move in this direction."

The fund was set up as a legal arm of the NAACP in 1939. But after the landmark Brown vs. Board of Education Supreme Court decision of 1954, the NAACP came under increasing pressure to separate its legal activities from its other functions.

In the early 1960s, differences developed between the two groups that could not be resolved. Some of those differences stemmed from confusion among contributors and confusion over who was responsible for various victories in the civil rights movement, especially the Brown decision, according to the court order.

In 1979, the NAACP convention authorized its board to revoke permission for the fund to use its initials. On Jan. 26, 1982, the NAACP registered the initials with the U.S. Patent and Trademark Office. The order issued yesterday stemmed from a case filed in U.S. District Court here May 25.

Hooks said yesterday that he anticipated no loss or gain in contributions as a result of the fund dropping the group's initials from its name. He said the NAACP still holds the fund in "in highest regard."

Hooks said, however, that he could foresee the possibility of future differences between the two organizations.

"The NAACP just has to speak with one voice," Wilson added.

Coleman said there had been very few instances where the two organizations have disagreed, and he said the fund's historic identity could be lost through a name change and that change could lead to a loss of money to other defense funds of various names.

Joseph L. Rauh, a lawyer who has handled civil rights cases for both organizations, said yesterday that he regretted the appeal, which he said he feared would stymie future civil rights activities.

"There's enough racism left in the country," Rauh said. "If you don't believe me, just go to Chicago."

"If there are those who say we have disturbed the peace," Hooks said, "it was a very uneasy peace and a very unjust unity. So now we have corrected that situation."

The lawyers for the NAACP in the case included former senator Edward W. Brooke (R-Mass.). Vernon E. Jordan, former director of the National Urban League, was one of the lawyers for the fund.

No monetary damages were sought or awarded in the case. The NAACP declined to say how much the suit had cost.