WASHINGTON -With the blessing of the Canadian government, a group this week started airing advertisements on Washington television stations warning that stiff tariffs on Canadian softwood lumber are threatening the U.S. economy and relations between the two allies.

The U.S.-Canada Partnership for Growth, a coalition of Canadian lumber companies and U.S. home builders and developers, is orchestrating the $2 million ad campaign, which is being paid for with a grant from the Canadian government.

Touting the historically close trade relationship between the United States and Canada, the 30-second ads warn that the 27 percent tariff on softwood lumber imports “is damaging this relationship.”

“If left in place, it will harm both economies,” an announcer intones, as images of hard-working Canadians appear on the screen. “Weakening America’s biggest customer undermines American interests, too.”

The launch of the ads, which are airing regularly on affiliates of the major TV networks, was timed to coincide with meetings in Washington this week between U.S. and Canadian trade officials, who are trying to resolve the decades-old dispute over the bilateral lumber trade.

U.S. lumber companies accuse Canada’s federal and provincial governments of effectively subsidizing the Canadian lumber industry through lower fees to chop down trees on government-owned land. The result, U.S. companies say, is that Canadian lumber companies can keep their prices below their American competitors, thus driving them out of business.

In response to pressure from U.S. lumber companies, the Bush administration last year slapped 27 percent tariffs on all Canadian softwood lumber imports. The American companies want the tariffs to stay in place until Canadian companies no longer enjoy help from their government.

The Canadian government and lumber companies say the tariffs are excessive, and U.S. home builders and other groups representing lumber-reliant industries complain the tariffs are inflating costs and hurting business.

The bilateral trade meetings ended Thursday, but the TV ads are scheduled to continue running in Washington for the rest of February, a partnership spokeswoman said. In addition, full-page ads are appearing in several Washington newspapers.

The partnership soon will launch similar print and electronic ad campaigns elsewhere in the United States, although it has not yet selected media markets.

“Letting [people] know that this is an expensive process that’s going on … is a very good start for getting some support for a resolution to the issue,” said partnership co-chair William E. Brock, a former U.S. trade representative and Republican senator from Tennessee. “I think you get a faster solution when people think what’s going on is wrong and needs to be corrected.”

Backers of the 27 percent tariff scoff at the notion that the ads will be effective in swaying negotiators who are well versed on the softwood lumber dispute.

“We’re not concerned by the ads,” said Scott Shotwell, executive director of the Coalition for Fair Lumber Imports, a Washington-based advocacy group. “We think people on Capitol Hill and decision-makers know who funds the ads and what they’re about.”

Julie Cram, a spokeswoman for the Commerce Department agency that handled this week’s trade talks, said she had not seen the ads but doubted they would influence decision-makers.

Others argued that the ads show that the tariffs have achieved their purpose: forcing Canada to face the consequences of its subsidization of the lumber industry.

“Ads on softwood lumber demonstrate that the U.S. stance on resolving this dispute is having an effect on Canada,” said Dave Lackey, a spokesman for Republican Sen. Olympia J. Snowe of Maine. “It’s actually welcome news that the Canadian government and industry have engaged in this issue; the tariffs have gotten [their] attention.”