Poland appeared set for a new period of tension after underground leaders of the suspended independent trade union Solidarity began a new campaign of opposition demonstrations against the country's military rulers.
Crowds gathered on Saturday and Sunday in the main square in Warsaw singing religious songs and sometimes raising their hands in a V-for-victory sign. The fugitive leader of Solidarity in the Warsaw region, Zbigniew Bujak, made a dramatic appeal for support in a tape-recorded message played in a cemetery where thousands of people had gathered to pay their respects to those who died in the Warsaw uprising of 1944, which was crushed by occupying Nazi German forces.
Mr. Bujak and four other Solidarity officials in hiding circulated a statement last weekend rejecting the government's plans for a gradual dismantling of martial law and calling for the establishment of a broad-based underground movement. The statement included the following assessment of Polish government actions:
* There was no amnesty for more than 2,000 people arrested or sentenced for violating martial law decrees and, although many internees had been released, top Solidarity leaders including Lech Walesa were kept in detention.
* There was no indication when the suspension of Solidarity would be lifted or of when the trade union issue would be resolved.
* There was no attempt to create conditions for national accord. The union leaders rejected as a controlled body the government-sponsored Patriotic Movement for National Rebirth.
* There were no concrete plans for economic recovery, except making people work harder and putting responsibility for the problem on the people.
In Des Moines, President Reagan told the National Corn Growers Association Monday that sanctions against Moscow and Warsaw might be lifted because ''martial law may be relaxing'' in Poland. He added, ''There is still no cause to celebrate in Poland.''