Dulles International Airport, generally rewarded as one of the nation's outstanding architectured designs since it opened 16 years ago, began undergoing its first major renovation this week.

Half of the airport's loading gates have been closed, and all passengers arriving during the busiest (4-9p.m.) are being transfered from their planes to a temporary building beneath the terminal's starkly modern tower.

The start of the two-year, $7 million expansion project, which ultimately will extend the terminal 50 feet to the south, resulted in some confusion and inconvenience Thursday and yesterday for the 10,000 travellers who use the airport daily.

Many arriving passengers missed new signs directing them to baggage handling stations and airport officials, who had the scene video-taped, quickly rearranged direction markers to make them more visible.

Workmen were still hammering at the temporary building minutes before the first passengers passed through at 4 p.m. Thursday.

Yesterday, the airport closed all 12 gates on the east end of the terminal and shifted all departures to the 12 west gates.

One result was heavy crowding in the loading area during the peak hours of 4 p.m. to 9p.m., when Dulles handles about 40 percent of its total traffic.

While there was some confusion and crowding, officials said the new procedures caused few additional problems.

Richard Griesbach, assistant to the airport manager, credited much of the ease in making the change to the airport's use of mobile lounges to move departing passengers between the terminal and waiting planes.

Griesbach said that the east gates would be closed for about one year, until work is completed on that end of the 50-foot extension. When it is completed, passenger traffic will be rerouted to the east gates and the west gates will be closed.

In about two years, th e temporary arrival gates will be torn down and both ends of the building will be put back in use.

The 50-foot extension will double the size of underground baggage-handling areas and ease crowding in the main terminal beneath the distinctive wing-like roof.