A large delegation of American congressmen, their spouses and staff aides flew into Tokyo yesterday for a postelection, government paid trip to a hastily organized unofficial symposium.

Preparations for the trip were made quietly, apparently for fear that voters would not take it kindly if news of the trip got back to the United States before the election.

The symposium, organized almost singlehandedly by one prominent Japanese politician, provides a week of talks between Japanese and U.S. legislators. Unlike other such international gatherings, it has not been officially established by Japan's parliament or the U.S. Congress.

Even by the Expansive standards of postelection congressional junkets, it is drawing a large American crowd. The latest list of participants has 41 congressmen, 43 staff members and 34 wives, although it was not clear whether all would come.

Some were arriving yesterday or later this week aboard three special military planes and others are coming on commercial flights. All are whisked by U.S. Embassy automobiles to Tokyo's most elegant hotel, the Okura, where 92 rooms were reserved for their use.

The U.S. Embassy here, which arranged accommodations, made no announcement of the visit as it usually does when large delegations come on public business.

The main organizer, of the symposium, Eiichi Nakao, a member of the Japanese parliament, announced it only last Friday and said the announcement was held up until after the mid-term elections at the American's request. The name of the American congressmen participating were sent to Japan only after the election, he said. A source in the organizing committee said the U.S. side asked that the names be held back until after the election because of the possibility of criticism during the campaign.

House Armed Services Committee Chairman Mel Price said at a news conference last night that the trip was part of his committee's "overall duties" and would require no extra appropriations. Spouses, he said, are traveling along "at no extra expense to the government."

In a news release in Washington last week. Price said spouses of legislators were included in the trip for "reasons of protocol." What protocol was involved was unclear since Japanese politicians rarely bring their wives to official gatherings.

Price said the military air costs are taken care of "in the budget" and noted that the aircraft are manned by regular Air Force personnel. He said the purpose of the mission is in line with the duties of the various committees represented to investigate all matters covered by legislation they handle. A total of five committees are represented.

Members of at eight House committees have gone to Japan for the meeting. Only one senator, S. I. Hayakawa (R-Calif.), a member of the Agriculture Committee, was scheduled to attend.

The symposium was put together so hastily that the latest program does not list the names of speakers at the main sessions. The meetings will cover such subjects as defense, agriculture, fishing, science and technology, and trade.

It was arranged by a previously obscure organization called the Japan-United States Interlegislative Council, which lists Prime Minister Takeo Fukuda as honorary chairman and former prime minister Nobosuke Kishi as chairman. It has no official status as an arm of the Japanese parliament and is the handiwork largely of Nakao, according to sources familar with the planning.

An ambitious young member of Japan's lower house, Nakao is the leader of a small faction of hawkish members of the Liberal Democratic Party known as Seirankai, a group formed in 1973.

Nakao said he had hoped for several years to arrange such a symposium. He had planned to hold it last spring, but delayed it because the debate on the Panama Canal treaty prevented American delegates from coming.

He said the hastiness of preparations this time was due to uncertainty in the United States about the possibility of a postelection special session of Congress.

From the program listings, there seemed to be no special axes to grind. Panels will discuss such issues as "the basic structure of Japanese agriculture." Japan's fishing industry, and the energy needs of both countries.

Some activities seemed designed to stress Japan's views on such touchy issues as fishing grounds and beef imports. The U.S. 200-mile fishing zone has seriously affected Japan's fishing areas, and Japan is strenuously objecting to American demands that it buy more American beef.

One side excursion will take American legislators to a small cattle ranch in southern Japan in an effort to impress te Americans with the small scale of such ranches. The Japanese beef industry contends that it is so small and fragile that more American imports might wipe it out.

Armed Services Committee members will fly to the northern island of Hokkaido to inspect Japanese Self-Defense Forces in an area the Japanese consider most threatened by the Soviet Union.

Sources here said that the U.S. Congress had never passed a resolution formally authorizing attendance at the conference, as is customary in the case of international exchanges.

The Japanese parliament has not recognized it formally either, although one of its committees authorized the use of official buildings to hold meetings. Most of the staff work is being done by aides of the Liberal Democratic Party.

Of the 41 congressmen expected, only about 30 are here exclusively for the symposium. Others are passing through Japan en route to China or South Korea on other missions.

In Washington, a State Department official involved in organizing the trip declined to give the names of the congressmen going to Japan to attend the meeting.

"Our job here is merely to facilitate them," he said. "Whether they want their names released is their business not ours."

While it is not clear exactly how many congressmen will finally attend, sources at House committees and congressmen's offices said yesterday that the following 29 representatives had left for Japan to attend all or part of the meeting:

House Agriculture Committee: David Bowen (D-Miss), Jack High-tower (D-Tex.) and George Brown (D-Calif.).

Appropriations Committee: Joseph P. Addabbo (D-N.Y.), Clair Burgener (R-Calif.), Clarence D. Long (D-Md.), Joseph M. McDadge (R-Pa), Gunn Mc-Kay (D-Utath), Clarence E. Miller (R-Ohio), Ralph S. Regula (R-Ohio), and C.W. Bill Young (-Fla.).

Armed Services: Melvin Price (D-III.), Charles H. Wilson (D-Calif.), Richard C. White (D-Tex.), Bill Nichols (D-Ala.), Robert H. Mollohan (D-W. Va.), Larry McDonald (D-Ga.), Antonio Won Pat (delegate from Guam), Bob Wilson (R-Calif.), and Robert E. Badham (R-Calif.).

International Relations: Andy Ireland (D-Fla.).

Interstate and Foreign Commerce: Lionel Van Deerlin (D-Calif.).

Merchant Marine and Fisheries: John M. Murphy (D-N.Y.).

Science and Technology: John W. Wydler (R-N.Y.), Barry M. Goldwater Jr. (R-Calif.), and Mike McCormack (D-Wash.)

Ways and Means: James R. Jones (D-Okla.), Bill Frenzel (R-Minn.) and Sam Gibbons (D-Fla.)

All of the congressmen were relected in the Nov. 7 voting.