Proposed changes in the design of the Vietnam Veterans Memorial received cautious approval yesterday from the Commission of Fine Arts, but it remains to be seen whether the commission's action will satisfy critics of the original design.

The changes in architect Maya Lin's competition-winning design, worked out as a compromise by advocates and critics of the initial scheme, involve placing a flagpole and a statue of a serviceman at the memorial site in Constitution Gardens. Opponents, preferring a more traditional, heroic memorial, had interpreted Lin's abstract, V-shaped design as a statement of shame and dishonor.

In view of yesterday's commission action, the precise placement of these new features has now become the key issue in the controversy. In a carefully worded letter to Interior Secretary James G. Watt, whose approval is needed before construction of the memorial can begin, commission chairman J. Carter Brown said simply, "We believe it is possible to find a solution for adding those elements in such a way as to obtain approval of the Commission . . ."

Brown then suggested that the statue and flagpole serve as an "entry point" for the memorial in conjunction with a directory that will help visitors locate the names of Americans killed and missing in Vietnam. These 57,000-odd names are to be engraved in chronological order along the long, intersecting black granite walls of the memorial.

The commission's action is thus substantially different from that of the National Capital Planning Commission, which last week gave approval in "concept" to a very different placement of the statue, namely "within the area before the apex of the memorial."

In effect, the Commission of Fine Arts was bouncing the ball back into Watt's side of the court. It was the interior secretary who postponed construction of the memorial pending the commission's approval of the what he called the "design improvements" embodied in the compromise. Groundbreaking had been scheduled for March 1.

Cy Kammeier, executive director of the Marine Corps League, an institution whose criticism of Lin's design was in part responsible for the compromise proposal, yesterday objected to Brown's suggestion, pointing out that it could mean a statue and flagpole that were "apart or separate from the memorial." At the invitation of Sen. John Warner (R-Va.), a longtime supporter of a Vietnam veterans memorial, proponents and critics will meet tomorrow in a closed session to consider the conflicting actions of the two federal design review agencies.