A banner-festooned auditorium echoed with the applause of a carefully selected crowd as Gen. Wojciech Jaruzelski stepped up to a podium, looked into a television camera and delivered a rallying speech to the nation here Wednesday.

Twenty-four hours later, a young man suddenly appeared on top of a low building in central Warsaw with a pair of loudspeakers while another specially invited audience of activists and journalists gathered in the busy intersection below. This time, they awaited a message from Zbigniew Bujak, underground leader of the banned trade union Solidarity.

So went the final rallies of Poland's hotly disputed campaign for Sunday's legislative election. Jaruzelski, his voice calm and his delivery almost perfunctory, recited a smooth appeal for citizens to participate in a vote that, he said, "will largely decide the shape of Poland in the next few years."

The Solidarity activist and three companions, in contrast, were arrested before they could broadcast Bujak's taped message. The rhetoric, however, was equally familiar: Bujak said the elections were meaningless and urged a boycott.

In the end, both sides in this most peculiar of Soviet Bloc election campaigns may have their way. Officials expect to report a turnout of up to 80 percent of Poland's 25 million eligible voters, allowing Jaruzelski to claim a popular mandate as he prepares for a more aggressive implementation of his political agenda. The government's measure of comparison is the turnout in last year's local elections, officially reported to be 75 percent.

Solidarity, which undoubtedly will dispute the government figures, once again has converted a Polish election into a meaningful political event in which a Communist government tacitly will acknowledge a dissenting minority of 20 percent or more. The union's standard of comparison is 1980, when 98.9 percent of Polish voters reportedly turned out in legislative elections a month before Solidarity's formation.

"For the government, the election has become a kind of referendum for normalization or against normalization," said Bronislaw Geremek, a historian and adviser to Solidarity leader Lech Walesa. "For Solidarity, the political importance of the election is simply that there will not be 99 percent participation. That proves that Poland is still different from the rest of Eastern Europe, and the future of Poland depends on preserving that difference."

In an apparent move to ensure control over Sunday's voting, authorities moved against Solidarity activists today, detaining and questioning leaders in four cities, opposition sources said.

Among those detained in Warsaw were former Solidarity spokesman Janusz Onyszkiewicz and two advisers to Walesa, Jacek Kuron and Zbigniew Romaszewski.

The continuing struggle between government and opponents has obscured the election's nominal purpose of choosing a 460-member legislature, or Sejm, for a five-year term. Following a reform of election laws similar to one adopted in the last local elections, two candidates will compete for each of 410 district seats, while 50 members of a prestigious national list, including Jaruzelski and other government leaders, will run unopposed.

Government officials pointed out that the new Sejm will greatly differ in composition from the body elected under the discredited leadership of former Communist Party leader Edward Gierek. Three-quarters of the new legislature will be made up of first-time members, and the number of noncommunist representatives will rise from 33 to 53.

Critics argue, however, that the changes are not a liberalization. None of the nonparty candidates is a known government critic, while every deputy who opposed the government on any significant issue in the last session has been excluded from the new candidates' list.

For the first time since the 1950s, the new Sejm also will not include Catholics who represent the views of the powerful church hierarchy. An unpublicized government effort to place up to two dozen such representatives in the new Sejm was turned down by the bishops' council. The church has since refused to take a public position on whether Poles should vote.

Despite these limitations, Polish officials say they view the election as a landmark in Jaruzelski's four-year-old leadership. The vote, they suggest, will be followed by a more aggressive approach by the leadership to opponents both inside and outside the party system.

Among the changes envisioned by government officials are a shake-up in government press and propaganda operations and reassignments in Jaruzelski's Cabinet.

While considering an amnesty for about 280 political prisoners, the government will continue its tough approach to Solidarity activists and apply more pressure for cooperation on both the church and conservative party sectors that have resisted a program of economic reform, these sources indicated.

Official campaigning has focused on more than 300 "consultations" and candidates' meetings around the country in which citizens have been invited to discuss a wide range of problems and offer advice to the new legislature.

Government officials also provided $6 million in supplemental funds to state television, which has mounted a propaganda campaign including variety and game shows featuring candidates as well as more staid interviews and call-ins.

Opposition leaders, who have responded with a blitz of clandestine publicity calling for a boycott, say the soft official tactics of persuasion have gone hand-in-hand with intimidation and repression. Arrests of Solidarity activists have increased in recent months, and there have been numerous reports of efforts to pressure citizens into voting, Solidarity sources say.