Washington — Ever so slightly, analysts here say, South Korea's image both at home and abroad has been improving. Reasons include strong, steady pressure to democratize the nation from the government's political opposition (and, on a much more subdued level, from the United States); coming National Assembly elections; and Seoul's desire to serve as host of a well-attended 1988 Summer Olympic Games.
Although each is ever suspicious of the other's motives, South Korea and North Korea, after a long lapse, have resumed bilateral talks on trade. They have also reopened Red Cross talks aimed at reuniting as many as 10 million family members divided by the Korean war.
Such increased contact with the North could help Seoul avert a rumored Soviet-bloc boycott of the 1988 Olympics. Although South Korea has no formal diplomatic ties with much of the communist world, recently it has been working particularly hard to improve its relations with China and the Soviet Union and insists all are welcome at the Olympics.
Former US Ambassador to South Korea William Gleysteen describes Seoul's new external policy as cautious but generally ''flexible and enlightened.''
Also, although many basic human freedoms are still firmly denied South Koreans by the authoritarian government of President Chun Doo Hwan, the former Army general has recently taken a number of small steps toward liberalization:
* Just a few days ago, Seoul lifted the political-activities ban on 84 more South Koreans, a move officially ''welcomed'' by the US. The most vocal and formidable political opponents of President Chun's regime, however, are among the 15 South Koreans still under a ban. Yet the number is considerably down from the 835 who were banned from voting, giving speeches, or running for office when Chun abolished all existing political parties in 1980.
* So far, Chun has allowed the formation of the Council for the Promotion of Democracy, a new coalition made up of representatives of three of the strongest former political parties and aimed at achieving democratic reforms through a cautious dialogue with the government.
One of the coalition's co-chairmen is Kim Dae Jung, the charismatic former presidential candidate who was allowed to come to the United States two years ago for medical treatment. Mr. Kim faces the almost certain prospect of serving 17 more years in prison on a sedition conviction when he returns to Korea early next year.
* Under a new law, South Korea's college students are allowed to demonstrate on campus, and the number of campus protests is sharply up. Some have also chosen to test the limits of the government's tolerance for illegality by demonstrating off campus.
In separate instances recently, several hundred students stormed the headquarters of not only the ruling Democratic Justice Party, but also the Democratic Korea Party, the chief opposition group among the new, legal political parties organized with government help. Though some of the students arrested during the disturbances have demanded the right of a free trial, Chun's government has been more inclined lately to release them without pressing charges.
* Also, although press freedoms are still sharply curtailed, Seoul has allowed some coverage of student demonstrations for the first time. Some analysts here say that concession is largely aimed at isolating radical students from others on campus. The press reports consistently portray demonstrators as radicals bent on riots and overthrow of the government.
''There is partial discussion of the issues instead of having really no discussion at all,'' observes Korea scholar and former State Department official Gregory Henderson. But he cautions that in the overall picture, ''There are very few signs of liberalizing - and they are quite slow and slight.''
Analysts say the real test still lies ahead as to whether or not these steps represent cracks in Chun's authoritarian armor. ''It's still a little early to judge whether or not this liberalizing movement is another wave in a continuing trend or if it marks a sort of milestone,'' says Donald Macdonald, research professor of Korea studies at Georgetown University.
The new harmony along the northern border, for instance, was recently strained Nov. 28 when a Soviet defector crossed from the North into the demilitarized zone, causing a shootout which led to the death of one South Korean and three North Korean soldiers. It was worst such incident since 1976. Although North Korea promptly postponed the second round of economic talks, slated for Dec. 5, the incident is not yet viewed by US officials as a major setback.
Also, it is conceivable that President Chun could yet be persuaded to beat a retreat on his more lenient policy of campus protests and arrests. The students have become increasingly bolder. And if, as expected, Kim Dae Jung is imprisoned on his return, it could add cause to the students' agenda and fuel more protests.
Although analysts say such protests are unlikely to pose any serious challenge to the government, a decision by President Chun to tighten controls could cost him political support at home and tarnish his image abroad. National Assembly elections, which his government predicts students may try to disrupt, are expected to be held in February. How well the ruling party fares then will set the stage for the presidential elections of 1988 when Chun has pledged to step down.
Many South Koreans suspect he may renege on that promise. They recall that President Park Chung Hee broke a similar promise and that Syngman Rhee, South Korea's first elected president, was overthrown in a bloody student revolution in 1960 after trying to rig elections. No president since the country's 1948 independence has left the post peacefully.
But US officials seem inclined to accept President Chun at his word. ''We hope he'll step down and we have no indication he won't,'' says one State Department official. Last year, on his visit to Seoul, President Reagan warmly endorsed the principles of democracy on several public occasions and praised the South Korean President for his ''farsighted decision'' to step down in 1988.
Yet Kim Dae Jung and a number of other opposition leaders have been sharply critical of the United States for not speaking out more forcefully against the Chun government's violations of human rights and democratic freedoms. Some of them argue that the sizable presence of US troops in the South has compromised Washington's willingness to take a stronger moral stand.
US officials concede that Chun has a long way to go to achieve any measure of real democracy, but reason that they can do most toward that end by ''quiet diplomacy.'' Says one State Department official: ''We think it's been more effective than other strategies.''
Yet some analysts insist radical changes in South Korea's government system may be necessary before democratic reforms go any further. They cite the widespread, unpublicized practice of indoctrinating numerous South Koreans in such Confucian values as obedience to authority. Most students, for instance, take a required course in ethics in which they are taught that no imported brand of democracy from the West adequately fits South Korea's traditions or needs.