A memorandum spelling out a power struggle between top American painting conservators and leadership at the National Gallery of Art was sent yesterday to international, national and local leaders in the conservation field.

The conflict surfaced two weeks ago when Gallery Director J. Carter Brown announced to the staff that a moratorium had been placed on futher cleaning of paintings by the National Gallery conservators until the board of trustees meets in October.

But the undigned memo, apparently written by the Gallery's conservation staff, details a six-year struggle between the people who clean and restore the paintings in the museum and its board of trustees, particularly the board's president and the Gallery's chief benefactor, Paul Mellon.

The memorandum centers on three areas: the quality of the restoration of a Rubens purchased by the Gallery in 1971; the questions, asked "in an accusatory" manner by a visiting committee sent in last spring and the findings of that committee, which were acted on by the Gallery's leadership but never revealed to the conservators.

As one Gallery staff member put it, "My colleagues are still unaware of whatever charges have been brought against them."

"They should not wonder what the problems are," said Gallery director Brown, "because we discussed very openly the differences in philosophy which are at stake. No specific decision has been taken by the trustees; that will happen at the board meeting coming up in October."

But Mr. Mellon's philosophy has been asked based on surveying the field at large after quite a period of time."

Brown said that three committee members had "communicated to Mr.Mellon the impression they had, and they were negative - pointing out a difference in approach to the cleaning of pictures.

"One (the gallery conservator's approach) cleans flat under fluorescent light and [the] other (the committee members') on easels under natural light. The question is, are you dealing with an historic specimen or a work of art in its function as an esthetic object.

"My own view happens to be that consideration of natural light and the tonal balance of the work of art have been underemphasized in much of American conservation in recent decades."

he memo which does not deal with philosophical differences, was presented last night to a meeting of the Washington Conservation Guild. One Guild member explained that the situation "needs to be out in the open because it has many places. It appears to be a power play of some kind, and if they could do it here, they could do it anywhere."

"As to the question of "power,'" said Brown, "there should be no question in anyone's mind that the trustees hold the ultimate responsibility. That is where the buck stops. It is clear in the by-laws that the president of the board of trustees in this case Mr. Mellon, is the chief executive officer."

Senior American conservators have expressed concern about the situation at the National Gallery, for they view it as a potential threat to their philosophy of conservation training and practice.

The memo begins by speculating that the beginnings of the recent Gallery moratorium go back to 1971 when the National Gallery purchased a large painting by Peter Paul Rubens, generally referred to as the "Gerbier Family" from London dealer Sir Geoffrey Agnew.

"Ever since it was cleaned and restored there have been comments to the effect that the picture had been ruined in conservation," says the memo. The painting was in fact cleaned by the late, highly respected conservator, Richard Buck, in Oberlin

The Gallery's own in-house conservation department was not set up until the following year, 1972, and never worked on the Rubens.

In May 1977, the memo said, Gallery Assistant Director Charles Parkhurst invited Briton John Brealey, the new paintings conservator at the Metropolitan Museum of Art, to meet the conservators.

"Brealey was known to be an outspoken critic of art conservation practices in America, and was advising the Andrew Mellon Foundation on conservation," according to the memo.

"During that visit he criticized U.S. training programs and cleaning methods at the National Gallery."

Reached in New York, Brealey was outspoken on the subject, though he said he had not actually looked at any of the paintings which the National Gallery had worked on, but found their "philosophy" disturbing.

In January 1978, the trustees visited the lab and seemed "receptive and made positive comments about the work," according to the memo. "However, it was later learned that Mellon had unofficially raised with some trustees the question of having others from the outside look over the work," the memo said.

In May 1978, a committee of three arrived Sir Geoffrey Agnew, the British Art dealer, British art historian Michael Jaffe, a Rubens scholar, and Mario Modestini, a Private New York restorer. The staff presumed they had come to advice on the Rubens.

The memo states that their questions were "accusatory" and in one instance, "one of the conservators was accused of abrading the signature on a painting he had never worked on."

"In early June," according to the memo, "the painting conservators were told that a moratorium had been placed on all future cleaning, and that Modestini was acting as Mellon's personnal adviser on conservation.

On Modestini's recommendation, Gabrielle Kopelman, a private conservator in New York, would be asked to come to the Gallery in the fall as a full-time conservator of paintings, the memo said. Carter Brown confirmed that Kopelman had been approached.

Kopelman, the memo continues, "would eventually train apprentices who would be chosen from art schools, not conservation institutes."

The memo concludes: "Although no charges of malpractice have been brought against the conservation staff, their future at the National Gallery is clearly uncertain."

The memo was addressed to Sheldon Keck, president of the International Institute of Conservation; Paul Banks, president of the American Institute of Conservation, and Stuart Treviranus, president of the Washington Conservation Guild. A copy also has been sent to Robert Feller, president of the National Conservation Advisory Council, a group presently advising the Congress on conservation priorities in the country.

In May, the American Association of Museums published "Museum Ethics," a slim volume three years in the making, which tries to define the age-old battleground between museum directors and trustees, and who really is in charge.

"Trustees should not attempt to act in their individual capacities. All actions should be taken as a board, committee or sub-committee, or otherwise inconformance with the bylaws or applicable resolutions," the report said.

Reached for comment last night, Carter Brown said, "There is no question of trustee interference here. Under the bylaws of this institution Paul Mellon, as president of the board, is the chief executive officer of the National Gallery of Art, even over the director. There is absolutely no question about that."