TOKYO, JULY 23 -- North Korea today proposed a troop reduction plan that it said could reduce tensions on the Korean peninsula and eventually lead toward unification with the noncommunist South.

The plan, according to a North Korean press agency report monitored here this afternoon, calls for the two Koreas to shrink their armies to fewer than 100,000 troops within the next five years. North Korea said it would unilaterally demobilize 100,000 soldiers by the end of this year as a sign of good faith.

Once both forces are reduced, according to the North Korean plan, the United States would have to withdraw its forces from the South and remove the nuclear weapons military analysts believe are maintained there.

The United States neither confirms nor denies the presence of nuclear weapons in South Korea.

North Korea currently musters a force of more than 800,000 men, according to western analysts. South Korea faces that army across the Demilitarized Zone with 600,000 men under arms, aided by more than 40,000 U.S. troops.

South Korea tonight had not reacted officially to the latest proposal from the North. But analysts and officials here and in Seoul privately expressed skepticism, saying the offer seemed aimed at gaining publicity rather than improving relations.

"Every time South Korean politics become unstable, they make some kind of peaceful attack," one analyst said.

The South Korean government believes its security depends on the presence of U.S. troops and is suspicious of any plan that would send them home. North Korea, on the other hand, tries to play on nationalist and anti-American sentiment in the South by urging the withdrawal of all U.S. forces.

Even before today's offer a senior western diplomat in Seoul had predicted a new "peace offensive" from the North. He said South Korea's recent progress toward democracy had frustrated the communist North, as had the North's inability thus far to disrupt or substantially share in the 1988 Summer Olympics to be held in Seoul next year.

Except for sporadic discussions about sharing the Olympic Games, there have been no substantive talks between the two Koreas since North Korean leader Kim Il Sung broke off negotiations in early 1986. Since then, the North has proposed three-way discussions involving the United States, while U.S. and South Korean officials have insisted that initial talks should be solely between the Koreas.

Today's proposal said that multilateral negotations should begin next March in Geneva, with the United States taking part. South Korean officials therefore dismissed the plan as a rewarmed version of one they have already rejected.

In the wake of large-scale street demonstrations in June, South Korean President Chun Doo Hwan promised free elections and other democratic reform for the South, where military coups and martial law have been more the norm during the past 40 years. Diplomats in Seoul said that if the South successfully moves toward democracy, North Korean propaganda efforts will be severely harmed.

"It gives them a real problem," one diplomat said, "and the one thing they can still really appeal to is the peace thing, and especially the nuclear thing."

Korea was divided after World War II, with the Soviet Union supporting the North and the United States supporting the South. The two Koreas fought a brutal civil war from 1950 to 1953, with U.S. troops fighting Chinese soldiers. The war left the border virtually unmoved, and the two countries have remained hostile neighbors ever since.