A section of the new terminal planned in National Airport's $735 million renovation would block the control tower's view of planes landing and taking off on one runway, which may require relocating the terminal, rerouting roads and refiguring plans for parking garages.

Federal Aviation Administration rules require that controllers be able to see the entire runway.

"We've been a little surprised at the complexity of the issue," said Linwood Holton Jr., chairman of the airports authority board, "but I don't think this is something we can't work out."

Board members said the renovation plans approved in 1988 were intended only as a guideline, not precise architectural drawings, and they expected that changes would be required over time.

Although staff members said they have known for some time that the plan would need to be changed, some board members said they were surprised to learn of the problem recently.

Among the remedies being considered for the flaw in the plan, airport officials said, are moving the whole terminal farther to the west, a costly plan that would put the terminal next to the Metro station.

Moving the terminal also would require relocating a proposed two-level road west of the station.

Officials had planned to put the road between the station and the terminal.

"If we moved {the new terminal} back it would certainly cost more; how much more, we don't know," said Carrington Williams, chairman of the board's planning committee, which next week is expected to receive a list of possible solutions from the authority's staff and a team that includes renowned architect Cesar Pelli, which the authority hired last year to design the new $200 million terminal.

More radical possibilities include making National's control tower taller or moving it, which several airport officials oppose because it would affect the appearance of the airport's 49-year-old main building, which the authority plans to preserve.

"We're probably looking at additional expense and time," Williams said. "There are a number of questions that have to be looked at."

Initial plans for the new terminal were included in National's master plan, which outlines nearly a decade of planned renovations recently begun there.

In the plan, one of the new terminal's three arms would block air traffic controllers' view of the north end of Runway 15-33, a 5,189-foot strip used by commuter and private aircraft.

The solution to what airport and FAA officials call a "line of sight" problem may require several costly adjustments to the new 35-gate terminal, on which construction is scheduled to begin in 1992 and be completed two years later.

Moving the terminal site could create a domino effect that would reroute a proposed $35 million, two-level roadway that would serve the terminal, and possibly change designs for three planned parking garages, including a $29.8 million garage already under construction, officials said.

James A. Wilding, the authority's general manager, said he doubted that more radical solutions will be necessary, and said a solution may be as simple as repositioning the arm of the terminal that would block the tower's view of the runway.

"It's conceivable this could turn into something major," Wilding said. " . . . But right now we're thinking that there are solutions that are quite workable."

Wilding said that although moving National's control tower is an option that "remains on the list," he said it is a remote possibility because of the complications it would involve.

A plan to move the tower could involve a lengthy process in seeking approval from the FAA, and most airports officials are not eager to add such a construction project to the airport's renovation program.

Holton said changing the tower would affect the traditional look of the airport's old main terminal.

"I don't think there's any chance" of changing the tower, Holton said. " . . . . Moving the tower is the last thing I want to do."

Even if the problem does not require changing the terminal site, Wilding said, the idea of building the terminal closer to Metro is appealing, despite the fact that only about 15 percent of the people who use National take the subway.

"Clearly it is our desire in this design to have more people using Metro," Wilding said, referring to the authority's goal of having 25 percent of the airport's traffic use the rail system in the next decade.

But any plan to build the road on the opposite site of the Metro station from the new terminal is likely face opposition from airlines, most of which would prefer to have the road closer to the terminal for the convenience of their passengers.

"It would give us a little bit of heartbreak, because the majority of National passengers come by car and taxi," said Dick DeiTos, executive director of the Metropolitan Washington Airlines Committee, which serves as a liaison between airlines and the authority.

Wilding said the authority's staff has known about the problem for some time, but Williams and other board members said they became aware of it only recently.

Although changing some projects may add to the renovation program's cost, Williams indicated that he and other board members would spend more money if necessary.

"We're doing something that's going to be there for the next 50 years," Williams said. "We want to make sure we do it right."

Options include moving the terminal closer to the Metro station, thus realigning the road to the west of the Metro. Or, the norternmost finger of the new terminal could be realigned. BLOCKING THE VIEW

In initial plans for the $735 million renovation of National Airport, one of the new terminal's three arms would have blocked air traffic controllers' view of the north end of Runway 15-33, a 5,189-foot strip used by commuter and private aircraft. The Federal Aviation Administration requires that controllers be able to see the entire runway.