Canadian Prime Minister Pierre Elliott Trudeau said yesterday that while Canada regrets that Polish authorities have declared martial law, if military rule prevents a civil war in Poland "then I can't . . . say it is bad," news services reported.

Trudeau also said at his weekly news conference that Canada will not suspend food shipments to Poland, as the United States has done.

But the 35-nation Madrid conference, which is reviewing East-West detente, recessed until Feb. 9 in a mood of profound pessimism about the consequences of the Polish crisis.

In last plenary session before the break, Western delegates spoke out publicly against Warsaw's martial law and signaled that a continued deterioration of events in Poland could kill the detente process enshrined in the 1975 Helsinki Accords on Security and Cooperation in Europe, special correspondent Tom Burns reported from Madrid.

The U.S. delegation chief, Max Kampelman, reiterated President Reagan's characterization of Poland's state of emergency as a "gross violation" of the Helsinki principles. The British chief delegate, speaking on behalf of the 10 European Community members, warned that "oppressive measures" could not be employed to impose political conditions on a nation.

The representatives of the Eastern Bloc addressing the plenary repeated the theme posed by the Polish ambassador that there should be no interference in internal affairs.

The Associated Press quoted Austrian Chancellor Bruno Kreisky as saying in Vienna yesterday that his country will offer refuge to any Pole reaching Austria's eastern borders.