The South Korean who was bludgeoned to death three weeks ago was listed officially as a cultural attache assigned to Seoul's consulate in this port city in Russia's Far East.

But practically everyone in the tiny community of diplomats here knew that Choi Duk Keun's work had little to do with opera and ballet. Like the handful of other South Korean consular officials in Vladivostok, he spent much of his time monitoring the several thousand North Koreans living in the region, one of the largest concentrations of North Koreans anywhere outside their homeland.

"All of our officers are concerned with collecting information on North Korea," said one South Korean consular officer here.

Choi's occupation, as well as heightened tensions on the Korean peninsula in the last month, has generated suspicions that his Oct. 1 slaying may have been the work of North Korean agents. Still, no evidence has come to light implicating North Korea, and the Pyongyang government has denied any involvement.

But South Korean officials and other diplomats say they cannot think of a more likely explanation for the slaying and the mysterious circumstances that surround it.

Some say they believe Choi's killing may have been ordered by Pyongyang as revenge for the deaths of a group of North Korean commandos whose submarine ran aground off South Korea's east coast Sept. 18. The commandos slipped ashore, some disguised in South Korean uniforms, but 22 of the 26 infiltrators were killed.

Choi, 54, was killed days later. Although Vladivostok has a reputation as a city with a high rate of violent crime and robbery, his slaying seemed suspicious from the start.

He was attacked in the stairwell of his apartment building and hit on the head at least eight times with a blunt object. Blood was found on the staircase from the sixth floor to the third floor. Police said Choi was also stabbed twice in the torso with a sharp object, which they said may also have been used to inject a poison. That led to speculation that the killers could have been professional assassins.

Police who discovered his body on the third floor found the equivalent of $1,200 in cash in his pockets, as well as a passport and documents. That ruled out robbery as a motive, but Russian investigators have so far been tight-lipped about their progress.

"Many people agree that it was organized in advance and carried out by professionals," said a diplomat. "But we have no evidence at the moment."

Like other high-profile murders in Russia in recent years, the investigation is going slowly. Autopsy results are not expected before mid-November. Although police have not spoken of any suspects, they did report that a witness saw at least two Asian-looking men running from the scene.

The killing caused jitters among South Korean diplomats in Vladivostok, who are trying to move to more secure residences. In Seoul, the government said it would beef up security for its diplomats around the world. But the work of monitoring North Koreans is continuing in Vladivostok, which is about 100 miles from the North Korean border.

Most of the North Koreans in the Russian Far East are poorly paid workers on government contracts in construction sites and timber camps. Officially there are about 3,000 North Koreans in the region, including several hundred in Vladivostok, but diplomats believe there actually may be three times that number.

They are widely regarded as better construction workers than the Russians, who often are less efficient because of high rates of alcoholism. North Korean laborers recently completed a high-rise apartment building for fishery workers here.

Many of the North Koreans are paid the equivalent of $10 to $15 a month plus room and board. Although the workers are closely monitored by crew chiefs, a handful still manage to defect to South Korea every year.

"But I still think they are happier than the rest of their family left at home in North Korea," said a diplomat.