The proposed National Harbor resort in Prince George's County received a major boost this week from Congress, which approved legislation to exempt the 1 million-square-foot development by the Potomac River from further review by a federal planning board.

Reps. Steny H. Hoyer (D-Md.) and Albert R. Wynn (D-Md.) inserted a rider exempting the project into a $14.5 billion spending bill for federal land and cultural programs. The bill was passed by the House on a 225 to 200 vote late Thursday. The Senate had approved it earlier.

But the measure's fate is still in question because President Clinton has vowed to veto the spending bill because of unrelated provisions dealing with mining, ranching and oil interests.

If the measure survives negotiations between Congress and the White House, Maryland officials will have overcome a major hurdle to the upscale, 534-acre entertainment complex, allowing the project to go forward under prior county approval. The action also would remove the threat of environmental lawsuits tied to review by the 12-member National Capital Planning Commission.

The Planning Commission gained oversight a decade ago, when a previous developer traded for federal land at the site and area members of Congress expressed concern about how his plans might affect the capital skyline and air traffic to Reagan National Airport.

Yesterday, supporters applauded the effort to jump-start construction of the waterfront attraction. Development on the site just south of the Woodrow Wilson Bridge has been dogged by controversy for more than a decade because of environmental concerns.

"This project does and will comply with all state and federal rules," said Debra DeShong, spokeswoman for Hoyer. "This fight is not about the project conforming with environmental regulations. This is about a group of people who don't want development on that land, period."

Opponents replied that residents would be denied the results of a nearly complete commission study and decried an end run around environmental rules by politicians whose campaigns have been funded in part by development interests.

"We're concerned that [Hoyer] seems to be more intent on helping Virginia developer Milton [V.] Peterson than in looking out for the best interests of the citizens of Maryland," said Frank Fox, Sierra Club D.C. metropolitan representative.

Peterson Cos. Senior Vice President Lynne Hansen said the Fairfax-based company appreciates the help from Maryland officials, including Gov. Parris N. Glendening (D) and Sen. Paul S. Sarbanes (D).

"The National Capital Planning Commission is an extraordinary layer of additional review that no one else doing development along the Potomac River has," Hansen said, adding that Prince George's County should be put "on par" with nearby jurisdictions.