For the frequent international traveler who lives in Tokyo, March 30 looms as a grim day. It is the date established for the opening of the new Tokyo International Airport, which will inherit almost all of Tokyo's international air service from Haneda airport.

For any other city in the world, the switch from a grubby, crowded terminal like Haneda to a spacious modern facility would be a cause for celebration. Among Tokyo's traveling people, it is as welcome as the great earthquake of 1923.

The problem is that the new airport is 38 miles from downtown, Tokyo and accessible only to the most determined. It is already known widely as the world's most inconvenient airport and getting to it will require expert planning. Haneda is a 30-minute taxi ride from the Tokyo for which the fare is $12. A taxi to the new terminal will cost $47 and entail a two-or three-hour ride through bumper-to-bumper traffic Except for distant transoceanic flights, ground time will equal or exceed time in the air. A two-hour flight to Seoul, South Korea could be preceded by a four-hour ground trip to Tokyo International for many passengers.

THERE ARE TWO possible train routes, but both of them are inconvenient for baggage-laden passengers. One takes only an hour but leaves from a remote station in East Tokyo.Another leaves from centrally located Tokyo station, but doesn't go to the airport. Instead, it drops one off in the town of Narita, 25 minutes by cab from the terminal.

Japan Air Lines recommends that its passengers use the bus service from the Tokyo city air terminal as the most promising route. That requires checking in at the air terminal at least two and a half hours before flight time and preferably earlier. The rider is supposed to take comfort in the knowledge that his plane will not take off until all buses have struggled through traffic jams to the airport.

Businessmen are making elaborate plans to beat the ground-time hassle. One executive of an American company will spend the night in one of the airport's hotels when he is scheduled to leave on a flight the following morning.

Others have sketched out this bizarre alternative: catch a domestic flight out of old Haneda airport to Japan's other major international airport in Osaka and transfer there to an overseas carrier. If the connection is good, the Osaka route is faster and easier than battling one's way out to new Tokyo International.

PROBABLY THE ONLY beneficiary is China Airlines, which is owned by the Taiwan government. It will offer the only remaining international flights from handy Haneda because the Japanese government required it to remain there. Japan has a policy of segregating the two Chinas and Peking's airline will fly out of the new airport. As a result, the Taiwan airline is expected to pick up a lot of business for its flights to Taipei and Southeast Asia.

Even before it opens, the new airport has earned a reputation for trouble, violence, and wasted money.It was supposed to open seven years ago but the determined farmers of Chiba Prefecture surrendered their land grudgingly after lengthy law suits. Militant student radicals made the airport project a symbol of wanton government disregard for people's welfare. The joint protests of farmers and students threaten to disrupt opening day flights and there are dark rumors of frontal attacks on the control tower and fire bombs being thrown at reserve fuel tanks near the runways.

THE AIRPORT'S BUILDERS made no attempt to top off their long struggle with any architectural niceties. None of those sweeping, dramatic designs for them. New Tokyo International is about as graceful as a World War II bomber hanger: It is a two-story, flat-topped structure with four arms extending out to circular aircraft bays.

The arrival and departure areas are functionally serviceable - moving walkways will carry passengers to and from planes and the customs and immigration checkpoints are geared for quick exits. But there isn't anything pretty about it all. The color spectrum ranges all the way from pale gray to charcoal, creating an overall sense of drabness. A visitor last week had the curious impression that the terminal had been in use for years.

Airport managers, wearied by years of public criticism an violent protests, grimly explain the good points. New Tokyo International ultimately will be capable of handling twice the number of international flights that now pass through Haneda. Passenger accommodations are modern and a swift passage through the terminal checkpoints will replace Haneda's delays. Bags will come quickly from the planes to pick-up points inside. The incoming passenger will be whisked in no time at all from plane to arrival lounge.

And then begins his journey to downtown Tokyo.