PRAGUE, JUNE 6 -- Czechoslovakia's first open election campaign in more than four decades wound up dramatically today with the sudden detention and interrogation of former Communist Party chief Milos Jakes and at least four other former top Communists as part of an investigation into alleged theft of party funds and property.

The provisional Czechoslovak government also announced it had evidence that the top candidate of the reconstituted People's Party had been "compromised" by his association with the old Communist regime and demanded that he withdraw from the parliamentary race.

The revelations and their timing just two days before the country's first free, multi-party elections since 1946 seemed likely to strengthen the hand of Civic Forum, the dissident-led political movement that has managed the country since the November revolution that drove the country's Communist rulers from power. Recent opinion polls show Civic Forum and its leader, Acting President Vaclav Havel, headed for victory this weekend, but forum leaders have been strongly criticized for moving too slowly to investigate top former Communists.

The roundup of the old leadership began late Tuesday, when prosecutors picked up former party ideology chief Vasil Bilak at his home in Bratislava, capital of the Slovak Republic. Bilak is widely regarded as the man who invited Soviet-led Warsaw Pact troops into Czechoslovakia in 1968 to crush the "Prague Spring" reform movement, an allegation he has denied. In April, Czechoslovak prosecutors launched an investigation into the invasion, which they called a "criminal offense against peace."

In addition to Jakes and Bilak, authorities interrogated the party's former head of police and security, Rudolf Hegenbart, former party foreign policy chief Josef Lenart and senior party official Michal Stefanak. State television reported that former president Gustav Husak also had been questioned.

Prosecutors said the men were being questioned about evidence of "serious criminal activity," and state television quoted unnamed sources as saying that this involved illegal disbursement of Communist Party property and funds missing from party bank accounts. Some also were questioned about their role in the 1968 invasion.

With the exception of Bilak, who was still in custody late tonight, all the men were released after questioning. Under a law enacted by the Communists, the government may hold a person without charge for 48 hours.

Officials of Civic Forum and its Slovak counterpart, Public Against Violence, called the timing of the roundup coincidental. "Things like this are not the result of politics," said Martin Butera, an official of the Slovak group. "We do not intend to make a martyr out of anyone," said another official.

Jakes headed the Communist Party until Nov. 24, when he was ousted along with most other senior figures associated with the 1968 invasion and the 20 years of repression that followed. Jakes, Bilak and Lenart have been expelled from the party. Even so, their detention was seen as a blow to Communist stalwarts who have spent recent months trying to save the party from political oblivion while at the same time trying to hang on to as much party property as possible.

The government also announced tonight that People's Party leader Jiri Bartoncik must withdraw from the election because he has been "compromised" by his political past, which has come to mean here that information has surfaced linking him with abuses of the former regime.

The People's Party, for 40 years an ally of the ruling Communists, has tried to remake itself since the revolution around a center-right program. Recently, it formed an alliance with Czech and Slovak Christian Democratic parties.