National Airport's new terminal will cost up to $100 million more than expected and will take two to three years longer to build if it is moved to correct the original design that blocked the control tower's view of a runway, airport officials learned yesterday.

Included in that estimate is $16.5 million for redesigning three parking garages, including one already under construction, and a heating and cooling plant. It also includes the cost of repositioning a two-level road that would serve the terminal.

Airport authority board members said they now face the difficult choice of approving a drastic increase in the cost of the projects or finding a less expensive solution that might make the new terminal less appealing. Together, the projects account for nearly half the $735 million cost of National's renovation plan.

"It's time to see whether we can come up with a world-class terminal," Linwood Holton Jr., chairman of the airport authority board, said yesterday. "If we are limited to a very satisfactory, middle-of-the-road facility, then so be it."

For Metro users, the problem could lead to greater convenience. The proposed relocation site is next to the existing Metro station, meaning passengers could take the subway to National and walk directly from the train to airline ticket counters.

The airport's master plan contains a flaw, which staff members say they have known about for two years, that would have one of the planned terminal's three arms blocking air traffic controllers' view of the north end of Runway 15-33, a 5,189-foot strip used primarily by commuter and private aircraft, and its taxiway.

James A. Wilding, the authority's general manager, said its staff believes that minor design changes -- such as repositioning or shortening the northern arm of the new terminal -- would solve the problem.

"I tend to be convinced that you don't have to move the entire building to solve it," Wilding said.

A plan calling for a shorter northern arm was among those presented to the authority's Planning Committee yesterday by a team led by renowned architect Cesar Pelli, who was hired by the airport authority last year to design the terminal, which was originally scheduled to be completed in 1994.

According to Pelli's team, a solution that would not involve moving the terminal would require lowering the ceilings in two of the terminal's arms from nearly 20 feet to about 10 feet.

Several board members say the low ceilings would be unsightly and would detract from Pelli's design, which they hope will make the terminal a landmark for generations to come.

The lower ceilings also would force the moving of some of the terminal's 35 gates, which could anger airlines that have planned to be in certain areas of the terminal.

During yesterday's meeting, board members expressed more interest in two more expensive options, both of which would involve moving the terminal west so that it would be adjacent to the Metro station. Under the more expensive of those two options, the cost of the terminal would be $81 million higher than the plan that would not involve moving the terminal.

Airport officials originally planned to build a $35 million, two-level road between the Metro station and the terminal.

That road would be moved west of the Metro station if the terminal is moved.

The architects said that much of the cost of moving the terminal would come from making its design fit with the design of the Metro station, a challenge because the station site is not flat.

"Clearly, this would require some reworking, some reorganizations," said Pelli. "It's a costly operation, but we believe it's feasible."

Moving the terminal also could require a two- to three-year delay in construction of the terminal and surrounding projects, James W. Congdon, a member of the design team, said yesterday. Besides redesign and construction delays, new agreements with airlines and the Federal Aviation Administration could be necessary if the authority's master plan is changed.

Putting the terminal next to the Metro station would create an additional 100,000 square feet in the building, which the authority could lease as concession space to try to recoup some costs.

Moving the terminal site back from the runways also would create about 10 more acres of space on the airport's apron, which could sweeten the plan for any objecting airlines by giving them more room to operate.

Pelli's team did not offer presentations on several other options for solving the problem, including the possibility of raising the height of National's control tower or moving it to another site.

Although those options probably would be far less expensive than changing the site of the planned terminal, several board members have all but ruled out changing the tower, saying that to do so would upset renovation plans for National's 49-year-old main terminal building.

Members of the Planning Committee said yesterday they will hold a special meeting next week to discuss their options on the new terminal.

"We're faced with a trade-off of time and cost versus a quality facility," board member Ron M. Linton said.

"That's something we'll have to decide."