Preparing for this week's Washington talks with President Carter, Japanese Premier Takeo Fukuda recently called a rare Sunday meeting at this official residence. The sprightly 72-year-old premier kept a clutch of Japanese ambassadors and senior big resucrats answering this questions and running through their briefing papers for six hours. "He slighted the human rights of the officials," one participant joked later.

While neatly alluding to a likely subject of diagreement - Carter's forthright stance on moral diplomacy is too provocative for Japan - the official was conveying his satisfaction at something else: After a self-directed cram course, Fukuda is considered better prepared to meet the American President on an equal footing than any of his predecessors ever was. Accompanied by Foreign Minister Ichiro Hatoyama, Fukuda is to meet with Carter today and Tuesday.

With Vietnam no longer a trouble some issue and no immediate threat to world peace, the two leaders are expected to focus on global economic problems, in which Fukuda has indicated that he is ready to accept the responsibilities appropriate to the world's third-largest economic power, America's leading Pacific ally and its No. 1 trading partner.

The premier shruggs off as "minor" the differences between the two countries, such as the likely imposition of extra U.S. tariffs on Japanese color television exports. Anti-American feelings, once an important political issue in Japan, are dying fast. All five opposition parties have endorsed this meeting, and Fukuda expects it to boost the conservative ruling party's failing popularity with the firmly pro-American electorate.

A new confidence, even eagerness, to join the United States in a joint world role to tackle disarment, trade and energy problems is evident here. Japan is committed to a 6.7 per cent growth rate this year, the highest among the industrially advance nations. Fukuda plans to tell Carter that his government is ready to team with the United States and West Germany as the three "locomotive" nations to reinvigorate the drooping world economy.

There should also be a meeting of the minds of the American desire that Japan loosen that tight strings on its aid purse and make a larger contribution to stability in the Asian Pacific region. Japan is cautiously moving into a leadership role: When Fukuda asks Carter for assurance of a continued U.S. presence in Asia he will be speaking unofficially for the five member nations of the Association of Southeast Asian Nations (ASEAN).

In a recent speech, Fukuda provided two examples of Japan's growing assertiveness. Stability in Korea, he said, is a delicate balance held by four major powers. He listed the United States, Soviet Union, China, and, to the surprise of his listeners, Japan. Addressing another issue, he said he was sure that President Carter's Asia policies were not completely formulated yet because he, Fukuda, had not been consulted.

"I never heard a Japanese prime minister talk like that," marveled an American expert newly returned to Japan.

The major area of disagreement in this week's talks is expected to be on nuclear fuel reprocessing. Eager to curb the proliferation of nuclear weapons, the Carter administrations may ban the exportation of technology that allow the reprocessing of nuclear waste to produce plutonium - which can also be used to build nuclear bombs.

As a signatory to the nuclear Non-Proliferation Treaty, Japan believes that it should not be cut off from U.S. uranium or atomic technology if it goes ahead with reprocessing. Fukuda has said that "Nothing should be done to prevent the use of nuclear energy as a substitute energy source." He is expected to make the case "vigorously" with Carter, clearing the way for later talks when the administration's policy-making on nonproliferation is complete.

Japan has now acquiesced to Carter's plan for withdrawal of U.S. ground forced from South Korea over the next four to five years.

American and Japanese polices on human rights in Korea may diverge, however. Fukuda has declared carefully qualified support for Carter's views, yet is not expected to speak out against violations in Korea and other Asian neighbors. Japanese excesses during the occupation of the Korean Peninsula, and in China and other countries, are said to have effectively negated Tokyo's right to criticize. Also, the realities of Japan's situation as an unarmed, resource-poor nation dependent on trade are echoed in a foreign policy that puts keeping friendly relations with everyone above all else.

The Washington trip is a vital opportunity for Fukuda to strengthen his low prestige with Japanese voters and possibly salvage a victory for the Lockheed-tainted Liberal-Democratic Party in a July election. Fukuda became premier and leader of the conservative party, which has ruled Japan through most of the postwar era, after it suffered a startling election setback in December. Defeat in the coming upper house election, where government and opposition forces are almost balanced, is thought likely and would force the ruling party into an unprecedented coalition.

While Fukuda is not popular - a Kyodo News Service poll last month found that only 34 per cent of the voters support his Cabinet - Carter will not be playing host to a lame duck. Although the ruling party is currently in trouble over its Lockheed woes, an unseemly leadership struggle and difficulty in cranking up the Japanese economy, Fukuda's conservative will probably remain in power or be the major force in a colation for years to come.