Strikers closed down the last section of the Gdansk port Wednesday, and a convoy of more than 60 police vehicles and water cannons headed toward the city along the main road from Warsaw.

Riot police smashed barricades to break up a strike at a southern coal mine and cleared strikers from an idled bus depot in Szczecin, but opposition sources said a coal mine and a cement factory joined more than a dozen workplaces on strike.Confronted by an 8-day-old series of job actions posing the stiffest challenge to its rule since 1981, the Politburo urged Communist Party members "to counter attempts to stir illegal strikes," the state-run PAP news agency reported.

The stoppages have idled coal mines and factories employing about 100,000 workers. The strikers demand legalization of the Solidarity trade union movement, reinstatement of workers fired for union activity and wage increases.

PAP said the Politburo also decided to convene an extraordinary meeting of the policy-making Central Committee "in the nearest future."

Section 2 of the Gdansk port, a cargo-loading division that was the only one in the city still working, joined the strikes Wednesday, government and opposition spokesmen said.

Near Elblag, about 50 miles southeast of Gdansk, a long column of police vehicles assembled along the main highway leading to Gdansk, said Western reporters driving to Warsaw.

Solidarity leader Lech Walesa, taking part in a strike since Monday at the Lenin shipyard in Gdansk, rallied Wednesday with strikers there and at two nearby shipyards.

"It is you, the young people, who will renew Solidarity and renew the country," Walesa exhorted youthful strikers at the Repair Shipyard, according to a tape of the rally given to reporters.

In Szczecin, police Wednesday routed strikers from a bus depot, said Jozef Kowalczyk, spokesman for the Inter-Factory Strike Committee in the Baltic port. PAP said strikers left the Klonowice depot "at the call of security forces," leaving only the Dabie depot still on strike. On Monday, police raided three depots around the city and arrested strikers.

Police evicted 150 strikers from the Miesko mine in the Silesian town of Walbrzych in an assault Tuesday.