WARSAW, SEPT. 28 -- Vice President Bush gave the banned Solidarity trade union a dramatic public endorsement today, appearing with leader Lech Walesa before a cheering crowd and then using a national broadcast on Polish state-run television to call for "self-governing organizations" such as unions.

"A Pole is not a serf," Bush said in English and Polish in his televised address, which drew a sharp official reaction after the vice president mentioned Solidarity by name and implicitly challenged the communist government.

The statement followed an emotion-charged scene this morning at Warsaw's St. Stanislaw Kostka Church, where Bush laid a wreath on the grave of a pro-Solidarity martyr, the Rev. Jerzy Popieluszko, then stood with Walesa on a balcony and waved Solidarity's victory sign at a wildly enthusiastic crowd.

"I am proud to be standing next to Lech Walesa, a man so respected in the United States," Bush told the crowd of several thousand, who gathered in and around the church despite the early workday hour and heavy police security.

The crowd, the first to contain Solidarity supporters during the vice president's tour here, responded with chants for the banned union, Bush, Walesa and President Reagan. "We want Lech, not Wojciech," they shouted at one point, referring to Polish leader Gen. Wojciech Jaruzelski.

The church appearance was designed to boost Bush's presidential campaign as well as Solidarity. Aides of Bush gave special access to a camera crew hired by his campaign to film the vice president and the Solidarity leader in front of the tumultuous crowd. The church yard was bedecked with Solidarity banners.

The vice president's two politically charged public appearances easily overshadowed his third day of talks with government officials here and the signing of a science and technology agreement between the United States and Poland. Bush's ringing endorsement of Solidarity clearly offended the Jaruzelski government, which had hoped that Bush's trip would lead to a significant improvement in U.S.-Polish relations.

Communist authorities anticipated that Bush would endorse Solidarity and meet with Walesa. But the vice president went beyond the usual practice of western visitors here by appearing with the union leader in public and endorsing Solidarity before a crowd.

Immediately following Bush's television appearance, which was inserted into the widely viewed evening news, a commentator for the communist party newspaper Trybuna Ludu observed that while certain of Bush's remarks could be supported, the vice president "did not get rid of all {his} myths and illusions" about Poland during his visit. Later, authorities broadcast a half-hour television program featuring commentators who further criticized the speech.

One of the commentators suggested that Bush had made the remarks in the hope of attracting Polish-American support for the Republican Party.

"They were pretty words," said Maximilian Berezowski, a journalist who appeared on the program. "But what did they hide? A certain didacticism which is typical of Americans."

Walesa, who traveled from his home in the port city of Gdansk to meet Bush here and rode to the church in Bush's limousine, was jubilant after today's event. "I am truly surprised, but now I understand the greatness of America, which has such wonderful representatives," he told western reporters. "Mr. Bush is a great man who indeed deserves to lead a great nation."

Accompanying Bush through the church as the crowd chanted their names, Walesa turned to the vice president and said, "Why don't you stay here and run for president?"

The appearance of Bush with Walesa was ignored tonight by the state-operated media, which opened its television newscast with a report on Polish-Soviet relations. As Bush waited off-camera in the studio to make his speech, the Polish broadcaster gave an account of the vice president's day, focusing entirely on events that the Poles had insisted on placing in his schedule. Bush was shown wearing a white lab coat at a television factory and inspecting the royal castle here.

Today's conflicting imagery crowned a visit in which Bush and Jaruzelski were unable to advance U.S.-Polish relations beyond an enduring impasse over political and economic fundamentals. Yesterday, Bush announced a minor U.S. concession to Poland on the framework for negotiating the rescheduling of Poland's debts to the 17-member Paris Club of western creditors.

However, commentaries in the Polish press made clear today that Jaruzelski's government continued to be frustrated by its inability to win U.S. commitments for desperately needed international economic assistance. "Despite removing . . . artificial barriers, there is no sign of the business relations coming back to normal," the official PAP news agency said.

Bush reiterated in his speech tonight the U.S. position that further economic aid will not be forthcoming until Jaruzelski initiates additional political reforms.

"We recognize that initial steps have been taken toward economic reform and national reconciliation," Bush said. "As you move toward greater freedom and pluralism, we will seek new ways to be helpful."

The vice president spoke in English. His remarks had been translated into Polish by U.S. officials and were read without changes by a Polish announcer.

Officials said it was the first time that a high-ranking western official had been allowed to deliver an uncensored speech directly on Polish television, reflecting the efforts of the Jaruzelski government to allow more openness in national media.