An unusually intensive flurry of discussions between the United States and Canada ended yesterday with the announcement that Prime Minister Pierre Elliott Trudeau will visit here April 28 to continue the consultations.

According to Canadian Foreign Minister Allan MacEachen, Trudeau's visit will concentrate on preparations for the seven-nation economic summit scheduled for May 27-28 in Williamsburg, Va.

Trudeau's visit is one of a series that will bring West German Chancellor Helmut Kohl here late this week and is likely to include special one-day visits prior to the summit by Japanese Prime Minister Yasuhiro Nakasone and British Prime Minister Margaret Thatcher, according to State Department sources.

In the current discussions with Canada, MacEachen met with Secretary of State George P. Shultz Sunday night and yesterday and also met Vice President Bush. Among subjects discussed, MacEachen said, were acid rain, toxic wastes, bilateral trade issues and various global and regional problems.

MacEachen quoted Shultz as saying the United States intends to ask permission to test cruise missiles in Canada. He said he did not give an immediate response but, in a news conference, he recalled recent remarks by Trudeau suggesting that such a request would be approved.

In addition to MacEachen, Transportation Minister Jean-Luc Pepin has been here in recent days to discuss trucking and aviation issues, and Energy Minister Jean Chretien was here to discuss gas supplies and prices.

In Canada yesterday, Chretien announced an 11 percent drop in the export price of Canadian natural gas "to make it clear to our U.S. customers that we are willing to respond to international market conditions."