A school feud that has lasted six years and involved some of Arlington's most powerful leaders, ended yesterday when the county's public school superintendent, Larry Cuban, announced he would resign in March.

"Under the circumstances, he has survived a lot longer than I would have imagined," said county board chairman Walter Frankland, who plunged into Arlington politics six years ago to battle Cuban over a school issue.

The widely anticipated resignation reflected the political changes that have occurred in the county since Cuban and his Democratic-backed supporters lost control of the county government. His letter of resignation was addressed to the man who was the center of the 1975 dispute, school board chairman O.U. Johansen.

Cuban, then newly arrived in Arlington, tangled with Johansen, principal of Washington-Lee High School, seeking to place him in an administrative job. Frankland led a parent's group opposing Johansen's transfer to such a post.

The group lost their fight with Cuban, but Frankland, with the support of county Republicans, made the county schools a political issue. He wrestled a seat on the county board from the dominant Democratic-backed Arlingtonians for a Better County, and the GOP followed his victory with others that many said sealed Cuban's fate.

Last year, given his first chance to fill an empty seat on the county school board, Frankland chose Johansen. The two enemies, Cuban and Johansen, have barely maintained a professional civility since. "The relationship was never one that I would characterize as warm," said Johansen yesterday.

Cuban's departure will come 14 weeks before the expiration of his current contract and after nearly nine months of rumors he was looking elsewhere for work.

The 46-year-old Cuban will leave a job that pays $53,600 a year to accept a grant from the Department of Education to research contemporary classroom teaching techniques. Cuban's proposal for the 18-month study asks for $65,000. Though his proposal has been accepted, a U.S. official said yesterday that "we are still negotiating" over the size of the grant.

"This has been one of the most exciting postions I have held, but I need renewal," said Cuban, the author of four books on education. He had worked nine years as a teacher and administrator in District of Columbia schools before crossing the Potomac to become Arlington's superintendent.

During his years in Arlington, Cuban ran a school system forced to deal with problems caused by dwindling enrollment, increasing numbers of students who speak English as a second language and teacher unrest over pay and benefits. Few of his proposed solutions to these problems endeared him to Frankland, who repeatedly attacked the superintendent for what he said was a failure to teach "the basics."

Earlier this year, at a swearing-in ceremony at the County Court House, before an audience that included then-school board chairman Ann Broder, Frankland characterized Arlington schools as deteriorating and said the educational system lacked leadership.

Yesterday, Frankland said Cuban's lack of administrative experience caused the school system to be mismanaged -- but he placed the blame for that situation on the school board that appointed Cuban in 1974.

"Gracious to the end, isn't he," said Broder, who was a member of that board. "All you have to do is look at our test scores over the last seven years and you will see that we have done what . . . was considered impossible. We have maintained and improved test scores while the student body has become increasingly urbanized."

Cubann said yesterday he was not concerned about the effect his departure will have on the school system. "Arlington schools will not fall apart if I leave 14 weeks before the end of the school year," he said.

"It doesn't bother me," added Frankland, marking one of the few issues that the two men have agreed on in six years.