Two federal commissions denounced a 52-story office tower proposed for the shores of the Potomac River in southern Prince George's County yesterday, saying that the looming, glass-sided structure would dwarf the Washington Monument and dominate the skyline of the nation's capital.

The Commission of Fine Arts, led by National Gallery of Art director J. Carter Brown, and the National Capital Planning Commission voted in separate, unanimous actions, to ask Congress for help in protecting the Washington skyline from suburban structures similar to the PortAmerica project at Smoot Bay.

That action could take two forms, staff members of both commissions said. One would be legislation allowing some federal control over the parcel containing the $175 million tower; the second would be long-range guidelines, probably nonbinding, for heights of buildings around Washington.

The Planning Commission members, saying they had been misled by PortAmerica developer James T. Lewis about his plans to build a tower, also voted to oppose the structure at a hearing scheduled for May 1 before Prince George's planning officials. The members suggest in prepared testimony that the buildings be limited to 17 stories.

"This, to me, is a pure act of vandalism to the Washington skyline," said Frederick E. Hart, a sculptor and member of the Commission of Fine Arts.

The strong esthetic opposition to the tower -- which would become the tallest structure between New York and Atlanta -- amounts to advisory action only, because neither body has authority to veto its construction. Lewis, an Alexandria developer who also is building three 17-story towers at Tysons Corner, has gained zoning approval from Prince George's officials but still must submit specific design plans for review by the county planning board and County Council.

He also needs Federal Aviation Administration certification that the tower would not pose a hazard for planes using National Airport.

This is not the first time federal officials have objected to suburban skyscrapers. In 1978, the Justice Department, at the urging of then-secretary of the Interior Cecil D. Andrus, sued unsuccessfully to block construction of four Rosslyn high-rise buildings, including the 390-foot USA Today tower. That suit also alleged that the high-rises would overpower Washington's official monuments.

V. Paul Zanecki, attorney for the developer of PortAmerica, said yesterday's actions by the commissions were "premature and a slap in the face" because the plans will not be fully presented until the May hearing before Prince George's officials. "This is in Maryland; it is six miles away from the monument area," he said.

The proposed project, which includes 1,200 housing units, a marina, shops, hotel and waterfront promenade, has drawn favorable reviews from county officials, including County Executive Parris Glendening.

Despite yesterday's criticism by the two commissions, said county spokesman Tim Ayers, "we still think it's a valuable project. We expect it will be a landmark. I'm not sure, considering how many miles it is from the Washington Monument, whether height is a legitimate concern."

U.S. Sen. Charles McC. Mathias Jr. (R-Md.) asked the Fine Arts Commission to review the project, and commission secretary Charles H. Atherton said the panel would ask Mathias and other members of Congress to create a plan setting height guidelines for suburban buildings. Structures in the District are limited to a height of 130 feet -- except for certain downtown buildings that can rise to 160 feet -- under a 1910 law that has kept the Washington Monument, at about 555 feet, the tallest building in the area. The proposed PortAmerica skyscraper would be 750 feet tall and built on a 100-foot-high knoll.

The commissions also plan to urge Congress to consider extending a "memorandum of agreement" between the developer and federal planners to include controls on the tower. That agreement was signed in preparation for congressional action last year allowing access to the development over federal land. But it covered only the project's waterfront parcel, which excludes the tower.

Members of the National Capital Planning Commission expressed anger yesterday that Lewis had said nothing of his plans for a skyscraper in congressional hearings last summer. They said they learned through the newspaper that he had submitted plans for the tower shortly after the land-use legislation became law in December.

"After you work with a guy for a couple of years," said member James Parsons, "you begin to build a trust. That's the sadness of it."

Zanecki told the panel yesterday that the plans for the tower had evolved over a period of time and "there was really nothing on the table" at the time the project was before the commission. Also, in a letter to the commission staff, Lewis said he "went out of my way to make it clear that such a building was under consideration."

The planning commission voted to express its "dismay" and "total disapproval" of the tower at the upcoming county hearing. The fine arts commissioners objected in more colorful terms.

"I've never seen a more arrogant statement by an architect in my life, and a developer," said commission member Neil H. Porterfield, a professor of landscape architecture at Pennsylvania State University.

"I think it shows very bad manners," said Pascal Regan, a California sculptor.