WARSAW, DEC. 1 -- In a wild exchange before a live national television audience, maverick Polish presidential candidate Stanislaw Tyminski tonight threatened his opponent, Lech Walesa, with a black briefcase that he said contained incriminating evidence about Walesa's personal life.

"I have a lot of material, and I have it here, and some of it is very serious and of a personal nature," Tyminski said ominously, as a television camera zoomed close to show a shiny black leather briefcase near his feet. "Perhaps I can even meet eye to eye with the candidate to talk about it."

Walesa reacted quickly.

"I demand immediate publication of these documents, absolutely, right now," the Solidarity trade movement leader snapped, leaning forward across the long table where the two men sat separated by two moderators.

"Perhaps we can talk privately," Tyminski answered, apparently startled by Walesa's retort.

"No," Walesa said angrily. "If you accuse me, show the documents."

Tyminski never did, a pattern that was repeated several times during the tumultuous joint press conference.

Throughout the evening -- the first time the candidates in the Dec. 9 presidential runoff have appeared together -- Tyminski dodged questions about his alleged visits to Libya but admitted that several former Polish secret police colonels and lieutenant colonels are on his national and regional campaign staffs. Tyminski said he employed the onetime agents of the ousted Communist government as a matter of charity, "like Jesus when he invited Judas to become a member of his group."

Walesa, in turn, seemed embarrassed to be on the same platform with his rival, a Polish emigre who was virtually unknown in his native land before his surprise second-place finish behind Walesa in last Sunday's opening round of the election.

Taking care to look presidential -- at one point wiping a smile from his face when the camera turned toward him -- Walesa pledged his support for Poland's free-market reforms and repeated his allegation that Tyminski is a front man for those who want to return the Communists to power in Poland.

"There's no doubt that the movement called Solidarity must continue the reforms, and this movement will be never changed, even with millions of dollars from former secret police who act against it," Walesa said.

When Tyminski asked why Walesa persisted in trying to link him to Poland's former Communist "structures," Walesa replied, "Because you are trying to blackmail me with that suitcase."

Walesa said he would seek continuity between his government and that of outgoing Prime Minister Tadeusz Mazowiecki, a fellow Solidarity member who finished behind Tyminski in the first round of voting.

The latest opinion polls show Walesa well ahead of Tyminski with 58 percent support to Tyminski's 30 percent. Walesa has gained 18 points since the first round.

An endorsement by Poland's Roman Catholic bishops is expected to further erode the industrial and farm vote that gave Tyminski 23 percent of the first-round vote.

Walesa tonight called Tyminski, who holds Polish, Canadian and Peruvian citizenship, a "classic example" of what can happen in a country undergoing a difficult transition from communism to democracy. He predicted a disaster if Tyminski wins the runoff election.

"After one month, we'll ask, 'Is life better?' and 50 percent of industry will go on strike. A month after that, workers will transport the president {Tyminski} back to the Peruvian jungle," Walesa said.

Tyminski insisted that government computer records showing he had traveled to Libya could be attributed to mistaken identity. "There are in the Warsaw telephone books seven Stanislaw Tyminskis, and perhaps one of them went to Libya," he said.

Poland's Interior Ministry reported Friday that computerized immigration records show, with "little doubt," that Tyminski traveled through Libya seven times on his way to Poland during the 1980s.

Tyminski, who arrived in Poland last month after living in Canada and Peru for 21 years, tonight described himself as an independent candidate who had "absolutely no contact with the former regime."

He first claimed not to know of the presence of former Communist officials on his staff. "I never asked him about his past," he said of his closest adviser, a former correspondent for Trybuna Ludu, the newspaper of the Communist Party Central Committee.

He later said he employed members of the former secret police out of charity, adding, "If someone cooperates with someone outside our staff, it's not my problem." Tyminski added later, "We never ask questions."

After Tyminski's upset, the Mazowiecki government acknowledged that it had failed to sell Poland's painful austerity program to the poor and less educated, and the prime minister resigned. Observers also credited the size of the Tyminski vote to voter anger and confusion about Walesa's bitter attacks on the government in the early stages of the campaign.

But Walesa was unrepentant tonight, insisting that if he had not launched his "war at the top" last March and decided to run for president, Tyminski would have taken the presidency from Solidarity.