On a political landscape colored a dull grey, Yasuhiro Nakasone stands out like shiny spot of bright paint.

He calls other politicians "cowardly" for failing to face the issues he deems important. He says Japan's present leadership is "too old" and prime Minister Takeo Fukuda "lacks a positive nature." The peoples' will is blocked by a "wall" of obstinate bureaucrats protected by timid members of parliament. Among cautious politicians who celebrate the bland and the oblique, Nakasone says, "I am determined to challenge taboos and priviliges."

For several months, Nakasone, 60, has been doing just that in an unusual, highly charged campaign to become prime minister of Japan. Few think he has a chance and almost everyone but him believes he will finish a distant third in the preliminary voting of party members Monday. But a reasonably close challenge could position Nakasone for a realistic bid in the near future, so many who ignored him before are beginning to take notice.

Regarded as a conservative nationalist and a hawk. Nakasone heads a parliamentary faction of about 50 members on the right wing of the Liberal Democratic Party's executive board. He is adored by those who want a militarily stronger and more independent-acting Japan and feared by opposition leftists who see in him a renascent nationalism of the sort that led Japan into China in the 1930s and then into World War II.

Public opinion polls show him anchored fairly close to the mainstream of political preferences. He runs a close race in national popuartiy with Fukuda and slightly ahead of the prime minister's chief rival, Masayoshi Ohira. If the election were a truly national poll instead of the truncated party primary that it is, Nakasone might be a formidable contestant.

His strong point is a streak of populism rarely head in the Liberal Democratic Party, which generally supports big business. He claims to represent Japan's unorganized - those who don't get lifetime jobs with big companies or those unprotected by big unions.Early this year he traveled around Japan sleeping in the homes of farmers, fishermen, and labor union members. Last week he summed up his experiences before a group of admiring war veterans in the town of Takasaki.

"What I felt is that we have a kind of wall and the voices of people who are working hard and sweating do not pass through that wall," he said. The wall is composed of bureaucrats who never listen to ordinary people, he said, and it is the duty of politicians to pay attention. But his colleagues in the party are too timid, he maintains.

"The party itself has a tendency to flatter the bureaucrats," he declared.

Nakasone himself has held several top bureaucratic posts, as have his election opponents, Fukuda and Ohira. A veteran of the Imperial Navy, Naksone was first elected to parliament in 1947. While steadily building up his own party faction in the legislature, he also has served as minister of both transportation and international trade and industry, director general of science and technology ad head of the Defese Agency. He also has held two top positions in the party, where he both supports and exerts pressure on Fukuda.

The "taboos" he chooses to talk about range from the serious to the trivial. He urges revision of the constitution to give legitimacy to Japan's armed forces, which heoretically are outlawed under the postwar constitution left behind by the American occupation. On the trivial side, he advocates legalizing the old imperial calendar system of naming years in accordance with the terms of presiding experors. Both are issues which other politicians usually avoid because they might revive charges of imperial militarism.

In a recent interview, Nakasone explained that he thinks constitutional revision is necessary if Japan's armed forces are ever to be accepted by the public. He complained that the Supreme Court dodged the issue by saying that armies are the concern of other branches of government.

"At the minimum, the self-defense forces should be recognized by the Supreme Court, and let the Japanese people realize that," he added.

But Nakasone's specific positions on military issues do not vary widely from the Fukuda government's. He does not favor eliminating from the constitution the section that renounces war as a national policy. He does no want Japan to begin buying long-range missiles and strategic bombers. He speaks of improving the defense forces "qualitatively" with newer antisubmarine and air defense equipment, which is also the government's position.

He would increase defense spending to about 3 percent of the gross national product as compared with the current 1 percent. But included under his 3 percent defense budget would be such measures as stockpiling of food and natural resources and aid to underdeveloped countries. Nakasone leaves the impression that he would not spend much the current budget calls for.

Nakasone's political ascent has been damaged recently by an assertion in a court deposition that he played a role in the Lockheed scandal that shook Japan a few years ago. An American company official testified that Nakasone received telephone instructions to intercede in Lockheed's behalf with government officials. Nakasone has emphatically denied the claim and has indicated he suspects the timing of the court deposition revelation may have been politiaclly motivated to harm him.

His future is also clouded by his own behavior. He is not widely liked within his own party and his proposal for a truly national election of a prime minister is unpopular. Many doubt that he could ever induce a majority of the party's members in parliament to support him, no matter what his national popularity may be, after all, they are the same people he calls cowards in his travels around the country.