The anti-American demonstrations here have suddenly gone poof. U.S. soldiers are walking the streets of Seoul again without looking over their shoulders. The official line from the South Korean government is: Yankees stay here.

Opposition to U.S. troops in South Korea that seemed to be boiling over has quieted dramatically in recent weeks, because of new threats from North Korea and a suggestion from Defense Secretary Donald H. Rumsfeld that U.S. troops may be cut and repositioned.

Resentment toward the U.S. government, however, has hardly disappeared. Outside the heavily guarded gate of the main U.S. military compound in Seoul, protesters sit daily with a loudspeaker blasting the English words "[Expletive] America!" over the camp. In a fourth-floor walkup office crammed with grim photos of Iraqi and Afghani civilians and other casualties of American wars, Park Jun Hyoung, a 34-year-old activist, explains, "We don't think of Americans as protectors. We think of them as occupiers."

But the mainstream South Korean public seemed sobered by Rumsfeld's remarks last week that the Pentagon might reduce its force of 37,000 troops and move some of them away from the front lines at the Demilitarized Zone, the frontier with North Korea.

The Korean critics "went up to the cliff, peered over, and then pulled back," said Scott Snyder, the head in Seoul of the Asia Foundation, a private, nongovernmental, grant-making organization.

Some people here fear that a relocation of U.S. troops would weaken defenses against hostile North Korea. Even more seem worried that it might undermine confidence in South Korea's suddenly vulnerable economy. And it could mean South Korea would have to spend more on its own defense.

Still other Koreans see a plot. A widely recounted theory here has the United States withdrawing its troops from the front lines with North Korea in order to remove them from harm when it attacks North Korea from another direction. But any significant movement of troops is likely years away, and a top U.S. Army officer calls the scenario "absolutely ludicrous."

Whatever the motivation, the prime minister of South Korea's two-week-old government made an unusual public plea to the U.S. ambassador on March 6 not to remove any troops until the current tensions with North Korea over its nuclear program are resolved.

The appeal by Prime Minister Goh Kun was all the more remarkable because he claimed to speak for the new South Korean president, Roh Moo Hyun. Roh had run on a platform promising more "balance" in South Korea's relationship with the United States, a phrase many of his supporters read as calling for a removal of troops.

The United States has kept troops in South Korea ever since the 1950-53 Korean War, both to protect South Korea from the North and to maintain U.S. power in Asia.

Various U.S. presidents have looked skeptically at that deployment. In 1971, President Richard M. Nixon reduced the troop strength from 60,000 to about 40,000. President Jimmy Carter sought to remove all but 14,000 troops, but was effectively blocked by his own aides, who opposed the idea.

The genesis of the current effort came during President George H.W. Bush's administration, when the Pentagon proposed moving troops now stationed near the Demilitarized Zone to points farther south. That was abruptly halted under President Bill Clinton when tensions flared in 1993 with North Korea over its nuclear ambitions.

Over the years, much of the tension with the U.S. military has revolved around its huge Yongsan base, which occupies a chunk of prime real estate in the center of the capital, Seoul. U.S. officials already are consolidating the hodgepodge of bases around the country, reducing the number from 41 to 23, and have been negotiating with South Korea to move out of Yongsan if they can agree on a suitable alternative and who would pay.

U.S. officials say they are sympathetic to the complaints. "If we had 6,000 South Korean soldiers in the middle of Washington, D.C., we might ask them to go elsewhere, too," Maj. Gen. George A. Higgins, assistant chief of staff for U.S. forces in Korea, said in an interview.

After Roh was swept into office with the help of the anti-military protests, Rumsfeld moved to press ahead with redeployments. He agreed in December to a joint study with the South Koreans, and last week predicted it would bring "some adjustments" in South Korea. "Whether the forces would come home, or whether they'd move farther south on the peninsula, or whether they would move to a neighboring area, are the kinds of things that are being sorted out," he said.

South Korea "has all the capability in the world of providing the kind of upfront deterrent that's needed," Rumsfeld said at a question-and-answer session with Pentagon civilians and troops.

U.S. officials say that modern military tools -- sophisticated intelligence-gathering equipment, unmanned drones and long-range weapons -- make foxholes near the front unnecessary.

"We have no intention of weakening our deterrent," U.S. Ambassador Thomas Hubbard told an audience of businessmen in Seoul this week.

That assurance hasn't stopped some Koreans from believing Rumsfeld's comments were spite for the anti-American protests, or a ploy to squelch the demonstrations. If they were, it worked.

"I think it was right, and justified, that we stood up with candlelight protests against American offenses," said Lee Young Joo, 29, a high school teacher. "And in the long term, I think the troops should leave. But right now is a very sensitive period, and I think they should stay."