SEOUL, JUNE 10 (WEDNESDAY) -- There was no suspense in the air when 8,600 delegates from South Korea's ruling party gathered in a Seoul gymnastics stadium today and nominated a candidate for president. Only one name appeared on the ballot -- Roh Tae Woo.

He is chairman of the party, a former four-star general, the personal choice of President Chun Doo Hwan. With the main opposition party planning to boycott the election scheduled for late this year, he is almost certain to become president next spring.

The lean and gray-haired Roh, 54, is considered likely to continue most of the basic policies of Chun. But many people here are asking whether his outgoing personal style could help forge a long-term conciliation with the opposition that has eluded the dour, imperious Chun.

In its four decades of existence, South Korea has never managed a peaceful transition of government. Without exception, presidents have taken office through assassination, street revolt or military coup.

Now, for the first time, a successor has been selected and is being groomed while an incumbent looks on. "These are important elements of optimism for Korea's political future," said Vice Minister of Culture and Information Choi Chang Yoon.

In the eyes of the opposition, however, one military dictator is simply handing power to another. It has called demonstrations today to protest the convention.

In a familiar response, the government has banned them as a threat to public order and put thousands of riot police on the streets to crush them before they can get under way.

Yesterday, busloads of police sealed off the Anglican cathedral in central Seoul where demonstrators were supposed to gather. About 40 senior dissident leaders reportedly were placed under house arrest. Police raided campuses and offices of opposition groups to confiscate leaflets, banners and street weapons and took similar steps to put down demonstrations called in provincial cities.

This morning, word spread that a student had died after being hit in the head by a tear-gas canister during a demonstration yesterday at a Seoul university. Although such protests often are violent, deaths are rare.

The careers of Chun and Roh have been linked closely since they were young men. Both were cadets in the elite 1955 class of the Korean Military Academy. Later both attended a special warfare training course at Fort Bragg, N.C., and commanded South Korean units in South Vietnam.

Both were junior generals in October 1979 when President Park Chung Hee was assassinated. Chun quickly began a bid for power. In December, Roh pulled a regiment under his command out of the Demilitarized Zone facing communist North Korea and sent it to Seoul to support Chun.

Later, with Chun's power consolidated, the two men resigned their commissions. Chun became president in August 1980 and the following year was elected for a seven-year term under a new constitution he drafted during martial law.

Roh claims to have been motivated by national service. "We did not grasp political power," he said in an interview last year. "It was entrusted to us. . . . I could not decide my destiny by myself."

He has since held a chain of important jobs: minister of internal affairs, minister of state for national security and foreign affairs, minister of sports, chairman of the Seoul Olympic Organizing Committee. In 1985, he became a member of the National Assembly and chairman of the ruling party.

With reporters, Roh sometimes displays classical learning, as Korean leaders are supposed to do under the Confucian tradition. One paper has reported an interest in western literature, too -- he was quoted as saying that as a cadet he memorized all of the poetry of Hermann Hesse.

Under his presidency, basic policies of close relations with the United States, export-oriented economic strategy, strong defense posture and cautious feelers toward communist North Korea are expected to continue with no significant change.

How will he handle domestic politics? In recent interviews, Roh has spoken of a need for leadership to emphasize "human relations" over rigid rules. "Democracy is not coercion but the fruition of dialogue and compromise," he was quoted as saying.

While this may be mere posturing, many Koreans suggest his comparatively open personality and experience in the past seven years have given him an outlook on problem-solving that differs significantly from Chun's.

While Chun has assumed an imperial detachment in the Blue House, as the presidential office is known, Roh has been meeting face to face with opposition members. Chun appears to view them mainly as enemies; to Roh they are real people with personalities. Chun's only contact with reporters are stage-managed press conferences once or twice a year. Roh banters with them frequently at his office.

Roh's wife and two grown children could be another plus. Chun's wife, Lee Soon Ja, has been considered a political liability for him ever since a relative was caught up in a black-market loan scandal in 1982.

Yet in some minds Roh will be just another military president, a continuation of seven years of Chun. Some people will never forgive him for helping Chun come to power and taking what they see as dangerous risks in doing so. "How can a man who pulled troops off the DMZ be president?" asked one Seoul resident.

The opposition also depicts Roh as sharing in culpability in the biggest single blot on Chun's standing with the public, the brutal suppression of antigovernment protests in Kwangju city in May 1980. More than 200 people died there.

Furthermore, Roh will be entering office -- through an electoral college system that is dismissed as rigged by many South Koreans -- in an election without participation by the main opposition party.