Solidarity leader Lech Walesa said today that the Polish government's account of a Central Intelligence Agency spy who fled with the plans for martial law here in 1981 proved that the suppression of the independent trade union was not a response to its provocative actions, as the government of Gen. Wojciech Jaruzelski has long contended.

Government spokesman Jerzy Urban's account yesterday of the defection of a member of the Army's general staff to the United States in early November 1981 showed that plans for martial law were laid well in advance of its declaration on Dec. 13 of that year, Walesa said.

He said Urban's account given to The Washington Post yesterday undermined previous official explanations of the crackdown. Jaruzelski and other top officials have insisted since 1981 that martial law was imposed in response to radical steps decided by Solidarity in early December.

"This would prove that martial law was unavoidable and was not due to the actions of Solidarity," Walesa told western reporters.

The agent, whom Urban named as Col. Wladyslaw Kuklinski, was deeply involved in the planning for martial law and provided the United States with detailed information about its planned implementation after fleeing Poland with CIA help on Nov. 6, 1981, according to sources in Washington.

Urban contended yesterday that the Reagan administration could have prevented imposition of martial law by warning Solidarity and the world of the plans. He said he believed the Reagan administration did not act because it had no real sympathy for Solidarity and foresaw violent upheavals here that it did not want to prevent.