Canada's Liberals pull out their secret weapon: 'the Rainmaker'

''The Rainmaker'' is back. That can only mean that the Liberal Party thinks it is in trouble as it approaches the Sept. 4 federal election in Canada.

''The Rainmaker'' is the nickname given Sen. Keith Davey, because this backroom political master can produce votes even when there is a political drought.

Senator Davey - a Canadian senator is appointed, not elected and Senator Davey earned his seat toiling for the Liberals - has been a key player in Liberal election victories for more than 20 years. He is being brought back as chairman of the Liberal campaign because it is in trouble. He replaces William Lee, who quit after a disagreement with Liberal Prime Minister John Turner.

The problem is more than Turner losing a televised debate in late July. There were ridings where the Liberals had not nominated a candidate weeks into the campaign, giving the opposition Progressive Conservatives and New Democrats an open field.

Senator Davey would never let that sort of thing happen. ''Where is Davey? These guys are in trouble,'' said a top Canadian businessman just days before Davey's appointment to the Liberal campaign was announced.

Well, Senator Davey is back, but his return is both a boon and an embarrassment for Prime Minister Turner.

During his race for the leadership of the Liberal Party Mr. Turner said there would be ''no rainmakers, no hit men'' when he was running the show, a direct reference to Senator Davey and other nonelected political advisers close to former Prime Minister Trudeau.

Mr. Turner had his answer after Mr. Davey's appointment. ''With me there are no rainmakers, but I get the best advice I can. Senator Davey has been helping me for a number of weeks. I'm in charge of this campaign.''

Liberal organizers put on a brave face and denied that Davey was being brought back to save the Liberals from an electoral disaster. The party is ahead in the polls, but none have been taken since Mr. Turner took a drubbing in the television debate.

Although the Liberals are putting on a brave face in public, they admit privately that the election campaign needs help, especially the detail work that an old political pro such as Davey can provide.

His political reputation rests on his having masterminded Pierre Trudeau's election victories. In 1980, Davey and others persuaded Trudeau to run again after the Conservatives had been briefly in power. The Liberals defeated the Tories under Joe Clark.

It was that 1980 victory that produced many critics of Davey, both inside and outside the Liberal Party. The campaign strategy centered on a Tory plan to raise the price of gasoline 18 cents a gallon. The Liberals fed on that economic fear but once in power raised the gasoline price even higher. It was seen as a cynical election ploy.

Conservative leader Brian Mulroney has ridiculed Davey's return to the fray. ''I think it's an indication of the serious problems they're having.''

The leader of the New Democratic Party, Edward Broadbent, who is doing surprisingly well in the campaign, was critical of the Rainmaker's reappearance.

''Once again they go to a man whose central concern has not been obviously about policy.''

Davey had been keeping a low political profile of late. He had been seen lingering over long lunches. Now that he is back in the saddle, the Liberal machine may start to hum and Davey will be hard at work, not at lunch.