TAEGU, SOUTH KOREA, OCT. 24 -- Radical protesters hurled dozens of firebombs at Roh Tae Woo, the ruling party's presidential candidate, as he campaigned in this generally progovernment city today.

Roh was not hit or injured, but the unprecedented attack indicated that a new trend of violence against Roh appears to be developing in South Korea's election campaign. The radicals may have been emboldened by a chain of anti-Roh disturbances that began two days ago in the Cholla region, a center of antigovernment sentiment.

In a rare show of accord, both the ruling and opposition parties condemned the campaign violence, warning that its spread could jeopardize the country's first contested election in 16 years, scheduled for December.

"If this kind of violence develops into major violence, it can disrupt the whole election process," said a top aide to Roh.

In an interview shortly after the firebomb attack, Roh said similar incidents might recur, but he tried to play down their importance.

"I believe the democratic process itself will not be disturbed by this kind of small incident," he said. Roh added that he "felt sorry" for the youths who threw the firebombs, claiming that they were "under instruction to do so." He refused to say whom he suspects of masterminding the attack. In the past, though, the ruling Democratic Justice Party has accused North Korea or the center-left opposition in South Korea of promoting antigovernment disturbances. Violence by protesters and the military has altered the course of Korean politics in the past.

Roh has been at the center of the sweeping changes in Korean politics in recent months. A close associate and military academy classmate of President Chun Doo Hwan, Rho was handpicked by Chun as his successor in June. This touched off massive public protests and battles between police and demonstrators. In the end, it was Roh who got Chun and the ruling party to accept the demonstrators' demands for free elections.

In the incidents earlier this week, one group of demonstrators pelted Roh with eggs and another threw tear-gas grenades at him. And before two of his campaign rallies, several hundred demonstrators battled with riot police forcing Roh to cancel one speech and delay another.

Security around Roh was tightened for today's motorcade and speech in Taegu, a large textile-producing city. Following today's attack, security is to be tightened even further.

The incident today was by far the most serious against Roh; some of his aides described the firebombing as potentially lethal. About 20 young demonstrators broke through the tight security cordon around Roh's motorcade and threw the molotov cocktails from as close as 35 yards from his open-backed jeep.

Police immediately arrested 10 of the protesters, believed to be students, according to local news reports.

The remaining demonstrators retreated to the nearby Kyungbuk University, where they were joined by several hundred students, who hurled rocks and scores of firebombs at the riot police massed in front of the university gates. During the two-hour skirmish the riot police fired volleys of tear gas. Small fires broke out in several stores on the street in front of the university gate.

Several hundred people gathered behind the police lines and cheered whenever a firebomb hit one of the policemen. The bystanders also jeered a camera crew from the state-controlled television station KBS, which the opposition has criticized for providing biased coverage in favor of the ruling party.

The clash at Kyungbuk ended before Roh left a nearby sports hall where he delivered a speech to about 10,000 people.

The firebombing attack marred what was to have been a triumphant homecoming by one of Taegu's best-known native sons. While the welcoming crowds were enthusiastic, the turnout appeared to be somewhat disappointing. Although aides to Roh said more than a million people had lined the city's streets during the motorcade to and from the sports hall, many observers said the figure was far less than that.

During his speech at the sports hall, Roh avoided any mention of the firebombing incident. But reflecting his criticism of the opposition as unable to maintain political calm in the country, Roh said, "Democracy without stability is worthless." And in an attempt to highlight his campaign's commitment to democracy, he added, "We can create a society where common sense, not authoritarianism, is the prevailing standard."

In the interview, Roh displayed irritation and disappointment over the firebombing incident.

"Radical elements tried to disgrace me in my own hometown," he said.

The violence could have a double-edged impact on Roh's candidacy. On the one hand, it could increase public support for him by depicting him as a victim of unjustified violence.

"The more they do such things, the more we get support because of sympathy," said one aide to Roh.

But on the other hand, some observers said, the incident could underscore the hostility that many people apparently feel for Roh, and this could weaken his stance as a candidate who would bring political stability to South Korea.