The airports authority board approved $30 million in construction projects yesterday for long-neglected National Airport as the first phase of a program to renovate one of the nation's busiest transportation facilities.

A 2,000-space parking structure, a new road and a two-level taxicab holding area will be the first projects for National with ground-breaking scheduled for spring. The Metropolitan Washington Airports Authority's plans already have drawn criticism from some area residents concerned that any improvements will serve only to worsen aircraft noise for the airport's neighbors.

The authority's board of directors also formally approved the previously announced $70.1 million in initial projects planned for Dulles International Airport, including a new road, taxiways, baggage claim areas and international arrivals area. The board also directed the airports staff to begin acquiring 900 acres adjacent to Dulles for construction of a fourth runway, west of and parallel to the two north-south runways.

The land, in Loudoun County, is expected to cost more than $50,000 per acre, said the authority's general manager, James A. Wilding, who recalled that the federal government paid an average of $350 per acre when it bought the airport property in the late 1950s.

The Dulles and National projects are the first of an estimated $1 billion in improvements envisioned during the next seven years. The authority board plans to issue bonds this winter to raise money for the projects, and voted yesterday to solicit bond underwriters.

The authority was created last year to finance and direct construction at the two airports, which until they were transferred to the authority depended on congressional appropriations for their spending money.

The authority has not adopted a master plan for National, but initial proposals include constructing a 32-gate terminal opposite the Metro station, on land now occupied by the 12-gate North Terminal.

The proposed terminal "would be a huge and costly white elephant, which the customers of {the authority} would have to cover in terms of user charges to be paid by the airlines, ticket costs to be paid by the traveling public and social costs of unwarranted overflight noise to be endured by area residents and visitors," according to a report by Citizens for the Abatement of Airport Noise Inc., a regional coalition of citizens organizations.

Airport officials argue that additional terminal space is needed to accommodate rising numbers of passengers, who complain of inadequate and uncomfortable ticketing space, baggage claim facilities, refreshment areas and restrooms.

Federal law does not allow air traffic at National to exceed 37 scheduled airline takeoffs or landings per hour.

"We're not expanding National Airport, we're making it better," said Sue Silverman, the authority's community relations director.

The number of passengers using National reached 15.6 million in the 12 months that ended Oct. 31, a 7.9 percent increase over the previous year, according to figures released yesterday. Some planning forecasts have estimated that the airport will serve 19.5 million in 2005.

Members of the antinoise group complained of lack of public participation in the plan's development. Wilding said his staff has held at least three public meetings on the plan and frequently discusses it with citizens groups and public officials.