SEOUL, OCT. 22 -- In an escalation of protests against Roh Tae Woo, the South Korean ruling party's presidential candidate, hundreds of stone-throwing demonstrators clashed today with tear-gas firing riot police at two provincial campaign rallies, forcing Roh to cancel one speech and delay another.

The incidents have sparked fears in the ruling Democratic Justice Party that more protests against Roh will break out as the December election nears and emotions grow sharper.

Ruling party secretary general Chung Suk Mo was quoted in local evening newspapers as saying the protests could become more radical. "That is what we had feared most about a direct presidential election," he said. "Such acts will occur more frequently."

Police authorities said they would crack down to prevent any further anti-Roh demonstrations. According to reports, the police plan to set up special investigative units that will aggressively pursue people considered directly and indirectly responsible for campaign protests. Already, 15 people reportedly have been arrested, and eight others are being sought by police for anti-Roh protests staged yesterday in Kwangju.

During the Kwangju protests, Roh was prevented from giving an impromptu speech after a tear gas grenade, thrown from a building, exploded near him. Choking on the tear gas, Roh was escorted away by security guards. In other incidents, he was pelted with eggs, and several protesters were said to have called out for his execution.

A former general and close ally of President Chun Doo Hwan, Roh is making a controversial campaign tour of the volatile Cholla region, a center of antigovernment sentiment. In 1980, the government acknowledged killing about 200 civilians in an uprising in Kwangju, the Cholla capital.

The incidents today occurred in Iri and Jongju, two adjacent towns in the Cholla region. In Iri, several hundred students reportedly clashed with police in front of the town railway station shortly before Roh was to deliver a speech there. As the students threw stones and shouted anti-Roh slogans, the police fired several volleys of tear gas. The rally and speech by Roh were delayed for about 30 minutes, news reports said.

In Jongju, at least 100 protesters demonstrated outside a gymnasium where Roh was to inaugurate a new campaign organization. Shouting "Roh Tae Woo, Murderer" and "Crush Roh Tae Woo," the protesters clashed with police firing tear gas and then retreated to a nearby church. Roh was forced to enter the gym through a back door, and he canceled a speech that he was to deliver outside the gym.

Roh, who was instrumental in pushing the government toward democratic reforms after weeks of violent street protests, is playing down his military background in the campaign. But many South Koreans, particularly those in Cholla, see little difference between him and Chun. Because he backed the coup that brought Chun to power, many South Koreans, especially in the Cholla region, hold Roh partly responsible for the bloody suppression of the 1980 Kwangju uprising.

In a separate development, the rift between the two opposition leaders, Kim Dae Jung and Kim Young Sam, appeared to widen after the two men held an inconclusive negotiating session.