Poland's political opposition suffered two major blows today when a slowdown in Gdansk's Lenin Shipyard drew only scant support and a top Solidarity underground leader surrendered to authorities.

Wladyslaw Hardek, a member of the five-man provisional coordinating commission of Solidarity's underground organization, appeared on Polish television tonight saying that further struggle was pointless and urging other fugitive leaders to give up.

His surrender marks one of the most serious setbacks to the underground movement since it announced its presence in April 1982, four months after the military takeover that suppressed the Solidarity movement.

Hardek's announcement came as Poles prepared to observe the third anniversary Aug. 31 of the 1980 agreement between workers and the state that gave rise to Solidarity after strikes at the Lenin Shipyard here. Shipyard employes today appeared to have shied away from a call by a secret workers' committee for a week-long slowdown.

Although several workers held open the possibility that a slowdown might yet develop later in the week, the protest appeared to founder in the face of employes' fears of pay losses and dismissals, Communist propaganda tactics and the already sluggish production pace in many factories.

The protest had been called to bring pressure on Communist officials to begin talks with former Solidarity chairman Lech Walesa. The government has ruled out negotiations with him and, in recent days, has launched instead a round of fresh attacks on Walesa's character and his tenure as union leader.

Walesa, arriving early this morning at the Gdansk shipyard where he is employed as an electrician, told reporters the slowdown "will go on."

When he emerged from the plant eight hours later, Walesa ducked questions about the protest's effectiveness, saying only: "Ask the people." But he passed out a typewritten statement rebutting government allegations that he is living in luxury on a fortune in U.S. dollars and operating against Polish interests as an American agent.

"I have never stood for confrontation," the statement said. "I have always favored argument and negotiation."

As the top Solidarity underground figure in Krakow and a one-time strike leader at the Nowa Huta steel mill, Hardek is the most senior fugitive opposition member to take advantage of the amnesty program offered by authorities with the abolition of martial law. According to official figures, 108 underground activists have surfaced under terms of the offer, which promises freedom from prosecution but requires the fugitive to confess crimes allegedly committed while underground.

Hardek said that "watching developments of the situation in Poland" he had reached the conclusion that the approach Solidarity's underground had chosen "brings harm." Protest actions, he said, "make workmates quarrel, lead to unnecessary divisions in communities, disturb the peace in cities and cause great material and moral losses."

Several dozen workers from different departments were questioned by western correspondents as employes streamed out of the shipyard after the morning shift today, but only four said they had joined or knew of any slowdown. The overwhelming majority said work had continued normally.

With large tourist groups swelling the number of those strolling through the city's reconstructed streets, the atmosphere in this Baltic port was generally relaxed.

"It's difficult to see whether people are working slowly," said one sandy-haired worker wearing a denim jacket. "Perhaps some action will be taken later."

While a number of workers expressed sympathy with the slowdown call, several observed that work in the yard had been slow for months as a result of severe shortages of supplies as well as widespread discontent with the government of Gen. Wojciech Jaruzelski. This unsteady, irregular work pace, they said, makes any coordinated slowdown action all the more difficult.

Said one young worker with a grin: "We always work more slowly. We have to look out for our health." Another remarked: "One way or another here, we work more slowly."

All the same, Polish authorities claimed the protest had flopped. "Work is going very well," said the shipyard spokesman, Stanislaw Czernielewski. "We have no complaints."

A report by the Polish press agency PAP said the Gdansk plant was using 10 percent more electricity today than last Tuesday, showing, it said, "more intensive and efficient work." Citing large plants in other cities where productivity was said to be on the rise, it concluded that "intensive work has been carried on in factories and offices throughout Poland" today.

But beneath the surface confidence, Communist officials appeared worried about the underground call and the prospect that it could spread.

Gdansk Communist Party leader Stanislaw Bejger visited the shipyard yesterday to highlight improvements in pay and the establishment of a worker self-management council, according to an official account published today, and government spokesman Jerzy Urban went to the facility today.

Following minor pro-Solidarity rallies here last week, provincial authorities have introduced stiffer measures against demonstrators until Sept. 15 and have ordered plants to keep tight control of worker discipline. New regulations enacted by the government in July when it formally ended martial law provide for jail terms of up to three years for those organizing protests.

An article headlined "Provocative ideas doomed to failure" was prominently played in Gdansk's two main papers today as well as in the main Warsaw government paper.

"Calls for production stoppages under the present conditions can be considered as an act of sabotage with its results turning against the society," the commentary said.

Nonetheless, a new leaflet by the clandestine Gdansk Shipyard Committee urged continuation of the slowdown until mid-September.

Walesa, in his statement, objected to government accusations that he had appealed for a slowdown. He also denied accusations that he had profited financially as Solidarity chairman.