Following a 20-day campaign conducted amid bitter cold and close government regulation, South Korean voters will elect a new National Assembly this month.

In many respects, the vote is shaping up as a test of two men who will not be on the ballot, President Chun Doo Hwan and dissident exile Kim Dae Jung.

Chun, a former Army general, is determined to see an orderly campaign and vote that will demonstrate popular support and political stability in his fifth year of rule.

But Kim, who is expected to return to South Korea four days before the Feb. 12 voting, has different plans. He appears to hope it will begin propelling him and the opposition to prominence.

Kim's return has presented a dilemma for Chun -- whether to arrest him and risk a popular reaction or to let him circulate and hope that people forget about him.

[A South Korean government spokesman read a statement to foreign correspondents Monday saying the government does not plan to arrest Kim upon his return, confirming reports that had reached Washington late last week. In a telephone interview Friday, Kim said he welcomed the news that he will not be imprisoned as an indication of "a reasonable attitude" on the part of Chun's government. "I will also respond with a reasonable and careful attitude when I go back," he said.]

Many members of the opposition here distrust Kim, but most seem to welcome his return as a means of giving focus to anti-Chun sentiments and lifting their camp's spirits.

Thus, some analysts see turbulent times ahead in South Korea, an important U.S. ally. "When Kim Dae Jung is back in the country," a western diplomat said, "tension is going to be higher."

Much could depend on whether the opposition succeeds in mobilizing South Korea's student population, traditionaly a potent force in politics but now relatively quiet.

But other analysts, including many in Chun's government, argue that Kim is a has-been, an opportunist who has little standing among the public and will have only marginal impact. He is dangerous, they say, not due to popularity but to an alleged willingness to use any means to gain power.

No one seriously expects that the election results will affect Chun's grip on politics here. "This is not a contention for power," said Lee Jong Ryool, spokesman for the ruling Democratic Justice Party. "This is a contention for control of the National Assembly."

Power in South Korea rests not there but in the Blue House, as the presidential mansion is known. Chun is now only halfway through a term that runs until 1988, when he has pledged to step down.

The campaign formally began in late January. By U.S. standards, it is not free. Although Chun has loosened some controls, 15 of the opposition's senior leaders remain banned from any participation in politics, the press is controlled and police agents loiter conspicuously outside dissidents' offices.

Controls extend to the minute details of a campaign. Recently, the government reportedly ruled that posters cannot allude to any association a candidate may have had with a banned politician. Slogans deemed too inflammatory are not allowed.

Chun's government maintains that such controls are necessary to bring order to an inherently chaotic political scene and rein in "irresponsible" and "demagogic" politicians who are prone to committing election fraud.

The threat from Communist North Korea, government officials argue, makes the speedy introduction of full democratic freedoms impossible.

But many dissident leaders see the controls as a means of preserving power for Chun.

In an interview last week, Kim Young Sam, a former opposition party president, charged that Chun's government is committing massive improprieties. It is exceeding spending limitations, using police and other officials to gather votes and limiting rallies to times when attendance is sure to be low, he said.

Before the campaign, dissidents considered a boycott, Kim Young Sam said, but rejected it after concluding that with a muzzled press, the public would not know why his side was staying away.

"Seats in the National Assembly are not important," he said. "What is important is to tell the citizens the truth and fight the present regime."

Chun came to power in 1980 in a military coup. He was elected president the following year under a constitution drafted with the supervision of his power group.

National Assembly elections were also held that year. Chun's party took about 35 percent of the vote. But under the complex election law, as the leading party in a multiparty legislature it was awarded 61 nonelective seats to give it a majority of 55 percent.

It is generally believed that Chun will retain about that number of seats.

In its campaign, the ruling party is stressing the relative calm of the past four years and South Korea's continuing economic growth, which registered about 8 percent last year.

Opposition candidates are focusing on continuing limitations on democratic freedoms and on Chun, whose legitimacy as president many never have recognized.

In particular, they demand that the constitution be amended to allow direct election of the president. Under the current system, it is done by an electoral college with more than 5,000 members, which they maintain is open to manipulation by the ruling party.

The opposition continues to have trouble in maintaining unity, however. There are currently three parties arrayed against Chun's one.

The most dynamic of the three is the New Korea Democratic Party, formed last month in Seoul after Chun lifted bans on 84 politicians. The party is commonly believed to represent Kim Dae Jung and Kim Young Sam, although neither holds formal office in it.

Turning aside pleas for unity, its members argued that the two existing opposition parties were tame, "court ladies" to Chun. By some accounts, they were also concerned that the top posts at the old parties were already filled.

Kim Dae Jung has spent the past two years in the United States, following his release in 1982 from a South Korean prison where he was serving a 20-year sentence after being convicted of sedition by a military court.

For the present, the big question is how the government will respond when he steps off a commercial flight around noon on Feb. 8, with about 20 sympathetic Americans and crowds of foreign journalists in tow.

World interest has been aroused by parallels between Kim and Philippine dissident leader Benigno Aquino, who was assassinated last year within seconds of stepping off a plane that brought him home from exile in the United States.

Officials in Chun's government contend that no one is more interested in Kim's safety than they. The government invariably would be blamed for anything that happened to him, they say. North Korean agents or local extremists might view his killing as an easy way to foment unrest.