Edwin O. Reischauer has been so deeply involved with Japan in so many ways for so many years that what amounts to an Old Boy Network has arisen around him.

Most of it seemed to be on hand last week to celebrate his 75th birthday by opening the Edwin O. Reischauer Center for East Asian Studies at the Johns Hopkins University School of Advanced International Studies (SAIS) here. The center on Massachusetts Avenue has been operating for more than a year, but on Tuesday it became official, with a symposium on our relations with Japan and a reception.

Reischauer, who has been called one of the best ambassadors this country ever had, went to Japan in 1961, just after anti-Eisenhower riots and the flight of presidential press secretary James Hagerty from an angry Tokyo crowd. When he left in 1966, the base had been laid for the planet's first true partnership between western and eastern nations.

When President Kennedy called on him in 1961, he says, "the job had never remotely occurred to me. I was a specialist in the 9th century, on the travels of a Japanese monk named Ennin in T'ang China. My wife was horrified. But I saw I was being asked to put up or shut up, after I'd been telling everybody what was wrong in Southeast Asia. I started out with great trepidation."

He shouldn't have been too astounded. He was born in Tokyo to missionary parents, soon became fluent in Asian languages, and by Kennedy's time was widely known as a pioneer, along with China historian John Fairbank, in introducing East Asia to Americans. His students fanned out over the country in a chain reaction, spreading his influence throughout academia and beyond to the political world.

As ambassador, one thing he realized that most Americans didn't was that Japan, for all its reputation as a feudal state, actually had been learning democracy since 1880, when local elections were first held there. Its first parliament was decreed in 1889. Furthermore, the feudalism itself had long since developed into a government by committee under figurehead leaders, preparing the people for action by group decision.

As for the much-discussed social hierarchy of Japan, "the country is light-years ahead of Britain as to class. It's virtually a classless society. Even America has a vastly more dictatorial society than they. Oh yes, they do honor the elderly -- which I'm beginning to think is a pretty good idea."

The scholar-diplomat flew in last week from his home in Belmont, Mass., with his wife, the former Haru Matsukata, to be feted by people with names like Fulbright and Acheson, Rockefeller and Mondale, Kennedy and Kennan. They were just a few of the thousands, including the Harvard undergraduates who took his famous Social Science 111, known to generations as "Rice Paddies," and others who went on to graduate studies under him. His Harvard tenure lasted from 1939, with significant breaks for intelligence and diplomatic service, until his retirement in 1981.

"He changed my life," says West Virginia's Sen. John D. Rockefeller IV. "I took the basic course at Harvard but I wanted more, I wanted to go somewhere, do something significant . . . In 1957 he sent me to the International Christian University outside Tokyo, and I was a student there three years, taught some English, but mainly I mastered the Japanese language. It was a fabulous three years."

"He was the best teacher I've ever known," says George R. Packard, dean of SAIS and Reischauer's special assistant at the embassy in Japan. "He taught me the most outside the classroom: just watching him work as ambassador. His main role, I think, was as a link to explain the Americans and Japanese to each other, especially in what he taught his fellow Americans."

Reischauer's greatest achievement, perhaps, was to persuade the U.S. military to give up jurisdiction over Okinawa, Packard says.

"The military was pledged never to let go of the island, where they had lost so many men in the war. Reischauer explained very quietly that our bases wouldn't be worth a damn because the surrounding population would make them unviable. There'd be a lot of hostility in a crisis, people lying down on the runways and all that. Somehow he talked them into it without loss of face."

In 1969 President Nixon signed an agreement with the Japanese under which we would keep our Okinawa bases, but without nuclear weapons. The island formally reverted to Japan in 1972.

"He can be a bit formidable, gruff and maybe shy at first," observes Packard, "but he has huge charm and a sense of humor that sneaks up on you."

Though there have been periods and administrations that didn't welcome Reischauer's strong opinions, it would be virtually impossible today to deal with Japan academically or politically without feeling his influence.

"No way could you avoid it, even if you didn't study with him," says Prof. Nathaniel B. Thayer, director of East Asian studies at SAIS, another veteran of the Tokyo embassy days and sometime Harvard colleague. "He was one of the few who were able to marry successful academic and public careers. He was in and out of the government all his life: in the war, as ambassador and later on a lot of temporary assignments."

Thayer says the Reischauer network includes the undergraduates who took "Rice Paddies," graduate students and other specialists. "Sooner or later everybody goes to Harvard for some reason," Thayer says, "and if you were interested in Japan you saw Reischauer."

The essential Reischauer message, he adds, is this: "Never never never be anything but wildly optimistic about Japan, about its capabilities, about what's going to happen next. And remember that our two countries are very very close."

Reischauer himself says he had three basic goals in his teaching: to make us aware that we really need to know more about the Far East ("that was enough of a goal for the first quarter-century"); to establish a world system built on international cooperation; and to find ways to expand this system to the other two-thirds of the world.

He sees no reason for Americans to panic over today's economic problems with Japan. "It's not remotely like what it was before the war. What we see now is nothing more than friction between two highly developed and integrated economies."

As the Japanese population grows older and retirees flood the nation, the increasingly independent-minded young are not exactly rushing to fill their jobs on the assembly lines or reenact their conformist lives, he says. As a result, Japan won't put so much pressure on the world economy in the future.

"They're still not really ready to join the world. They still feel themselves very separate. They realize it intellectually, but they still need to make that step."

When they do, he predicts, East and West will form what he calls the First World. "And it will only be a First World because Japan is in it."

"If I had time for a third career," Edwin Reischauer says, "it would be to help spread this out beyond the limits of race and culture to become a one-world concept. The great partnership of America and Japan is the model."