Tardy registration with the Justice Department as a foreign agent and possible conflict of interest during his stint as chairman of the International Trade Commission threaten to plague Daniel Minchew well beyond his present dilemma as a senator's accuser.

Almost two months before he quit his $50,000-a-year job at the ITC, Minchew signed a $10,000-a-month consulting contract with a group of Japanese businessmen.

Minchew reportedly did no work for the group until he left government, but his decision to sign a contract with a group of foreign businessmen while chairing the agency charged with arbitrating matters of foreign trade raises questions of conflict of interest.

Minchew's attorney, Robert Fierer of Atlanta, denied any conflict of interest and said his client not only told the ITC in "early 1978" of his intention to leave the agency later that year, but also performed no services for the Japanese business group while holding his government job. "If you look at his voting record with the ITC, you'll see he didn't act in any way to benefit the Japanese," Frierer said.

Minchew is the chief accuser of Sen. Herman E. Talmadge (D-Ga.), who is now before the Senate Select Committee on Ethics, charged with taking unauthorized reimbursements of Senate funds for personal expenses.

Minchew signed the contract to represent The Committee of Two Hundred Club Inc. of Tokyo on Aug. 11, 1978, although he did not leave the ITC until Oct. 1 of that year, according to documents on file with the Justice Department. He began negotiating with the Japanese several months before he signed the agreement, Minchew has told the Ethics Committee's special counsel.

The contract is signed by Minchew, who went from Talmadge's staff to the ITC post in 1974, and by Susumu Ogato, owner and president of the company.

Upon leaving the ITC to work for The Committee of Two Hundred Club, Minchew was to receive a $3,000-a-month retainer for 30 hours work a month between October and December 1978, according to the two-year contract. Between January and March, his fee was to jump to $5,000 a month, and from April until the contract expired, he was to be paid $10,000 a month for 25 hours of work a week. Any overtime was to be billed at the rate of $100 an hour, the contract specifies.

The Foreign-Agents Registration Act of 1938 required Minchew to file a copy of the contract with the government when he began representing the Japanese Oct. 1.He did not, however, register as a foreign agent until almost six months later, on March 26, 1978, records show.

The Justice Department has yet to decide whether to investigate Minchew for possible violations of the law. Violations carry civil and criminal penalties of up to $10,000 in fines and five years in jail.

"The whole thing is on ice until after the [Senate Ethics Committee] hearings are over," a department spokesman said.

Minchew has told the committee he set up and ran a secret account at the Riggs National Bank in 1973 and 1974. He told the committee that Talmadge knew of the account and ended up with some of the $39,000 that went into it. Talmadge has denied the allegation and called Minchew a "proven liar, cheat and embezzler."

Minchew is scheduled to testify before the committee today.

Talmadge's lawyers have tried to use Minchew's executive session testimony before the ethics panel, which acknowledged the lucrative arrangement he made while still at the ITC, in an attempt to discredit him as a witness.

Will Leonard, a former ITC chairman who served on the commission with Minchew and who is now in private law practice in Washington, said that in cases before the ITC involving Japan, Minchew "voted against them as much as for them."

The Committee of Two Hundred Club Inc. is composed of independent, medium-sized Japanese companies seeking export advice and access to federal government officials.

U.S. firms that have found it increasingly difficult to compete against merchandise made in Japan and elsewhere have charged in several cases that the Japanese firms have "dumped" goods on the American market, meaning the goods are sold here for less than it cost to produce them. Under U.S. trade law, the ITC rules on these and other charges.

Minchew's Japanese connection dates back to December 1969, when he began working as legislative director for the Washington-based Japanese-U.S. Trade Ouncil, a group the Japanese government set up in 1957 to carry out a massive propaganda campaign.

The council and its principals were charged in 1976 with violating the Foreign Agents Registration Act for misrepresenting themselves as a trade association when 90 percent of their funds were from the Japanese government. Without admitting or denying the allegations, the council agreed not to violate the act in the future.

Minchew joined Sen. Talmadge's staff in 1971. Gordon Roberts, the senator's press secretary, said Talmadge wrote a glowing letter on Minchew's behalf that helped his aide secure the ITC job in late 1974.

Since he resigned from the ITC, Minchew has spent at least $6,000 entertaining the Japanese in his $425,000 home in Chevy Chase, Md., the Justice Department documents show. On behalf of The Committee of Two Hundred Club, according to the documents, Minchew donated $100 to the Democratic National Committee, hired Ridgewell's in late February to cater two dinner parties that cost more than $800, and hired a limousine for a Japanese visitor for $200.

The nature of the Japanese group's business is to "promote better trade and cultural relations between Japan and the U.S. and to provide advice on ways of increasing imports of U.S. products and services into Japan and to provide notice of investment opportunities in the U.S.," Minchew's registration statement says.

His duties:

The contract calls for Minchew to provide a bimonthly report on "trade, economic, and political activities that affect the Japan-U.S. relationship and general information on political currents within the U.S.," as well as special additional information upon request.

Further duties include setting up seminars in Japan on trade, economic and political issues that affect foreign trade, and coordinating "meetings, interviews and schedules for Japanese groups or individuals sent to Washington" by the Two Hundred Club, the contract says. CAPTION: Picture, DANIEL MINCHEW . . . Sen. Talmadge's accuser