Mark MacGuigan, Canada's secretary of state for external affairs, yesterday proposed a special summit meeting of the seven major industrial democracies to discuss the additional strains on the "troubled western alliance" created by U.S. adoption of broad new trade sanctions to delay the Soviet natural gas pipeline.

In a "get-acquainted" meeting with Secretary of State George P. Shultz, MacGuigan urged a special summit meeting "to try to heal some of the wounds which seem to have developed" since the Versailles economic summit in June.

The United States appears headed for a showdown with its Western European allies over President Reagan's decision after the Versailles meeting to extend a ban on sales of U.S. oil and gas pipeline equipment to include overseas subsidiaries of U.S. companies and foreign firms producing the equipment under U.S. license.

"The problems we had to face at the summit now seem almost small" in comparison to the adoption of the trade sanctions and the decisions of Britain, France, Italy and West Germany to order or encourage their companies to defy the ban, MacGuigan said in a press conference after yesterday's meeting.

Shultz treated the suggestion "as an idea worth considering," MacGuigan said.