Solidarity leader Lech Walesa threatened to order a national "strike alert" Tuesday unless Poland's government reverses its decision to close the Lenin shipyard and shows itself willing to reinstate the banned labor federation. The statement Sunday was the strongest from Solidarity since communist authorities announced Oct. 31 that they intend next month to close the Gdansk shipyard, the free trade union movement's birthplace and political base. The closure announcement all but extinguished already dim prospects for round-table talks with Solidarity that the government had promised in exchange for Walesa's efforts to end an August strike wave. Now, Solidarity and the government appear to be on a collision course.