Under the cloudless autumn skies of this rural community in central Japan -- a clutch of small, hilly farms wedged between the country's Pacific Coast and its mountainous spine -- Masaaki Takeshita says he is fighting a battle he can't afford to lose against the United States.

At stake, according to the friendly, 38-year-old farmer, is the heavily mortagaged, 2 1/2-acre plot that has been in his family for three generations. Here, Takeshita raises a small herd of beef cattle and grows mandarin oranges, the two cash crops that, in a good year, yield an income of $15,000 and support his wife and two children.

"If big amounts of cheap American beef and oranges are allowed to flood into Japan," Takeshita says good-naturedly, "my whole life will simply be destroyed."

Takeshita, who is typical of many farmers in this country's inefficient agriculture sector, is speaking of a mounting drive by U.S. trade officials to get Japan to dismantle barriers to imports of beef, citrus fruits and other farm goods that protect local interests and keep lower priced American commodities from freely competing in the market here.

Agriculture, an area in which Japan now enforces import curbs by quotas on 22 products, has emerged as one of the potentially most explosive issues in the tense economic relations between the two countries. The United States, burdened with huge trade deficits with Japan, sees the quota as symbolic of the closed nature of the Japanese market that puts restraints on a broad range of imports. Washington has pressed Japan to act more quickly or face a protectionist backlash in Congress.

Senior Japanese officials argue that the American demands are hopelessly excessive because they ignore the realities of what is possible within the constraints of the country's political system, where farmers wield tremendous clout and will fight vigorously to keep the barricades from falling any time soon.

Japan's 5 million full-time farmers make up only 9 percent of the country's labor force, but are organized under a powerful nationwide umbrella group that has vowed to block any moves toward liberalization. The conservative Liberal Democratic Party, which has run the government here for 27 years, relies heavily on the farm vote, and tampering with the prerogatives of the agricultural lobby is politically risky.

Reflecting these pressures, the latest round of talks on two-way farm trade abruptly broke off in Honolulu last month after Japanese negotiators rejected an American call for Tokyo to eliminate import controls on beef and citrus fruit beginning in 1984. Instead, the Japanese reportedly have offered to cut import duties on a package of other commodities -- including papayas -- that are of little importance to American farmers.

In Mikkabi, a township of 16,000 where the economy is almost exclusively geared to the production of beef and citrus fruit, the dispute has churned up strong emotions. The walls of the local farmers' cooperative are plastered with colorful posters that depict Ronald Reagan, dressed as Superman, swooping down on the Japanese islands with a load of American beef and oranges only to be turned away by a more muscular Japanese farmer.

Satoshi Nakane, a local co-op official, admits that opening Japan to more farm imports would benefit the Japanese consumer, who now has to pay nearly three times more for a pound of beef than his American counterpart and about $2 for a pound of American oranges.

"But for the Japanese farmer," he says, "it's a matter of life and death. We can't afford to fight on an equal footing with the U.S." American farmers' larger, highly mechanized operations allow them to produce and market commodities at a fraction of the cost to the Japanese farmer.

In contrast to the wide-open spaces of the U.S. farm belt, farmers here grow mandarin oranges in tiny groves carved out of steep hillsides. Usually each tend a few head of beef cattle in cramped, tin-roofed pens in their backyards. In Japan, a string of volcanic islands with a land area roughly the size of Virginia and the Carolinas, only about 15 percent of the country is fit for farming and the mountains and rocky terrain bar the widespread use of labor-saving machinery.

Government attempts to get farmers to sell off their small-scale holdings to open the way for bigger, more efficient farms have met with stiff resistance in the Japanese hinterland because of a centuries-old tradition of hereditary ties to the land. At the same time, however, the productivity of farms has suffered in recent years, because of a flight of young people to the cities in search of more prestigious white-collar jobs, leaving the older generation behind to tend family plots.

In Mikkabi, farmers, some of whom belong to the local Lions' Club, stress that they harbor no personal animosity toward Americans, despite their heated opposition to U.S. trade demands. They still speak fondly of a teen-age American woman from their sister farm community in California who made a big hit here a couple of years ago as an exchange student at the community high school. Much of their ire is reserved for Japanese bureaucrats in Tokyo, who, they complain, lack comprehensive policies for bailing them out of their current difficulties.

"We've got nothing but bad advice from the government," says Nakane, who explains that local farmers plowed in their paddy fields in the early 1960s, when Tokyo encouraged them to go into mandarin orange production because of a surplus of rice. When overproduction of the citrus fruit led to plummeting prices a few years later, they borrowed money from the farmers' credit union to embark on cattle-raising, again at the behest of government.

After 15 years, complains another local official, "we're still trying to work off those debts and now there's no place to go."

According to senior bureaucrats and politicians here, it may take another decade before Tokyo can gradually iron out the deeply rooted troubles in the country's farm sector to allow the freer market access for imports Washington now wants.

In the meantime, they suggest that tough American bargaining tactics have whipped up a tempest in Japanese politics that may delay further the glacial pace of achieving a consensus on any public issue here that pits powerful interest groups against each other in Japan's strongly consensus-oriented society.

Fearing protectionist retaliation against Japanese industrial goods in the United States, the country's big-business establishment, a major source of financial support for the Liberal Democrats, publicly has endorsed the U.S. call for farm trade liberalization.

Leaders of Zenchu, the national farmers' organization, which reputedly indirectly controls the majority of votes in the conservative countryside, has bitterly countered that the country's industrialists are the chief culprit in Japan's troubled trade relations. Torrential exports of Japanese cars, electronic gadgetry and other manufactured goods, they argue, have unfairly put the spotlight of critics in the United States and Europe on Japanese agriculture.

"The onus of the trade problem," a Zenchu leaflet warns pointedly, "should not fall on Japan's farmers."

The hint has not been lost on the country's Liberal Democrats, who recently sailed a resolution through the Diet, or parliament, strongly opposing the freeing of trade in beef and citrus fruits. Such public fanfare, however, sounds less convincing these days to farmers like Mikkabi's Takeshita, who is fearful that industry's support for liberalization may soften the party's resolve to defend agricultural interests.