Poland's Roman Catholic bishops threw their weight behind Lech Walesa's presidential bid Friday, and a new opinion poll gave the Solidarity leader a big lead over outsider Stanislaw Tyminski.

The bishops told voters the election would be the "crowning act" of the anti-communist revolution led by the Solidarity union.It appeared to be a clear recommendation to the voters of the overwhelmingly Catholic country to vote for Walesa, who led the 10-year crusade that overthrew communism last year.

"Our collective participation in electing the president of our state is also a moral duty," the bishops said in a statement calling for a big turnout in the Dec. 9 runoff between Walesa and Tyminski.

Earlier, Walesa's campaign received another boost when the OBOP opinion poll, reported on state television, gave him a lengthening lead over Tyminski.

The poll, taken two days after Sunday's first-round vote, said 58 percent of voters had decided to cast their ballots for Walesa in the second round and 30 percent for Tyminski.

"Thank God," sighed a Walesa aide in the northern port of Gdansk when he heard the result.

The poll was the first since Tyminski scored a shock win in the first round over Catholic Prime Minister Tadeusz Mazowiecki and qualified to face Walesa in the runoff.