The National Park Service and the Air Line Pilots Association voiced strenuous objections yesterday to a proposed 52-story World Trade Center, the architectural landmark of the billion-dollar PortAmerica development on the Potomac River in Prince George's County.

In testimony submitted to the County Planning Board, National Park Service Regional Director Manus (Jack) Fish Jr. said the structure, which would be the tallest building between New York and Atlanta, would "permanently, irrevocably and severely" overshadow the capital's "monumental core."

Fish said he was also concerned that the tower, "if it is constructed, will set a standard which other developers will try to exceed, causing even more degradation to our unique and beautiful capital and its environs."

Michael L. Moore, a safety specialist representing the 34,000-member commercial pilots association, called the proposed tower "a terrible idea that will disrupt an already complex approach and departure environment for aircraft operating out of the Washington National Airport."

If the skyscraper is built at its proposed height, he said, it "will certainly endanger not only the crews and passengers of the aircraft but, very certainly, the people that will inhabit the proposed structure."

The height of the tower, on a small portion of the PortAmerica site south of the Wilson Bridge, was a major focal point during testimony before the County Planning Board, which listened yesterday to 11 hours of testimony on the mammoth waterfront development of 1.7 million square feet of office space, 1,200 town house and apartment units and a marina for up to 500 boats.

Approval of a general concept plan offered by developer James T. Lewis is the last major hurdle to the project, although the Federal Aviation Administration must still give its opinion on whether the skyscraper poses a hazard to flights operating in and out of National Airport.

At 10 last night, the county planners decided to resume their hearing and make a decision May 9.

Moore, of the Air Line Pilots Association, said the height of the tower, with a base 100 feet above sea level and with a 55-foot spire, is actually 905 feet above sea level.

Should the airport's precision instrument landing system not operate in inclement weather and low visibility, he said, planes would have to be diverted to other airports to avoid striking the tower.

"Aircraft having to break off the approach [to one runway and having to circle to reach another] due to strong wind conditions would be in danger of colliding with the building," he said. "The flight path of these aircraft would be directly over or very near to the proposed building.

"The construction of this building would be an unacceptable hazard to persons in the air and on the ground and would create a substantial adverse effect for virtually all of the instrument approaches" to two runways at National Airport, he said.

Bill Broadwater, an aviation consultant for PortAmerica, disputed Moore's contentions concerning airline safety. He said his firm had been retained to do a study that will provide more evidence to support the case for the skyscraper.

Several citizens spoke on behalf of the project. James Myrtle of the Prince George's County Economic Development Corp., a nonprofit firm that works to attract business to the county, called PortAmerica "probably the most significant development" in the area. He said the tower would "enhance the skyline, not detract from it."

Opposition to the tower on both safety and esthetic grounds has arisen since Lewis formally submitted his concept plan, including the skyscraper, to the County Planning Board in January.

In April, the National Capital Planning Commission, which has no direct jurisdiction over the decision, voted its disapproval.

Fish, in a letter to the planners read into the record, said the Park Service had expressed concern over the lack of height limits in a December 1982 County Council rezoning hearing. The following year, however, the council rezoned the land for the site without any such restrictions.

"When one looks across the Mall from the White House," Fish wrote, "One sees symbols of our great history -- monuments to Washington and Jefferson, with no competing structures that detract from them . . . . We fear that these symbols of our nation, which have dominated and formed the image most Americans envision when they think of Washington, would be significantly altered by construction of the 52-story tower . We think the Washington Monument should remain supreme on the skyline as it has for over 100 years . . . . "

Fish praised the rest of the overall plan for the development, made possible in part by a transfer of 55 acres owned by the Park Service that was approved by Congress.

County planners recommended approval of the overall plan, with 30 conditions including that the developer provide $150,000 for a fire department boat and other, mostly cosmetic changes. But the staff trod lightly on the height issue, urging only that the developer consider the criticism and study other options.