One year ago, when President Bush was up in the polls and his critics were down in the dumps, Washington strategist Jenny Backus said that her fellow Democrats badly needed to build “an amen choir,” a national network of activists who would sing the party tune at fever pitch, 24/7.

Well, she got her wish. An amen choir has been duly assembled. And here’s a glimpse of its latest handiwork, a controversial TV commercial that made its debut Wednesday in 17 key states, including Pennsylvania. Amid images of workers, children and flags, a narrator intones:

“Remember the American dream? … It’s about fighting for the middle class, not special interests. George Bush’s priorities are eroding the American dream. It’s time to take our country back from corporate greed and make America work for every American.”

This “issue ad” will probably cross your TV screen several times over the next two weeks, courtesy of its sponsor, the Media Fund — an “independent” political group with no official ties to the John Kerry campaign, even though the fund’s top guy is Harold Ickes, who ran President Bill Clinton’s 1996 re-election campaign.

And that’s just one group. Much to the Bush campaign’s dismay, the amen choir is amplifying Kerry’s message at a time when he is financially strapped and virtually incapable of airing his own ads.

Others in the choir are taking on Bush as well — notably MoveOn.org, the liberal cyberspace group, which just finished a week on the air in 17 states, including four TV stations in Philadelphia, telling viewers that “when it comes to choosing between corporate values and family values, George Bush is not on our side.”

That’s precisely why Democrats wanted a choir. They knew their candidate would emerge from the primaries with a fraction of Bush’s campaign money (Kerry is roughly $100 million behind Bush). And they didn’t want him to spend four long months, until the party convention in July, getting hammered by Bush TV ads.

So they needed extra megaphones — outside groups that could put ads on TV; a think tank that posts anti-Bush talking points on its Web site (the new Center for American Progress, helmed by another ex-Clinton aide); and some liberal talk-show hosts to balance the Rush Limbaughs (Air America Radio, starring Al Franken and others, starts March 31).

Republicans don’t seem upset about the new think tank or the talk-show hosts; they dominate in those areas. But they have dispatched lawyers to complain about the ads, because they think some of the groups are violating federal law.

Here’s the point of contention: “Independent” political groups can accept huge fat-cat donations (known as “soft money”) as long as they don’t coordinate their activities with any campaign, or urge the victory or defeat of any candidate.

The Media Fund, which is partly financed by wealthy liberal donors, hasn’t called for Bush’s defeat in its TV ad, but Bush lawyer Thomas Josefiak thinks this is all semantics. The ad, he wrote Tuesday in a letter to federal officials, “clearly attacks President Bush, an identified candidate for federal office, and is being broadcast in states commonly considered crucial to the outcome of this fall’s presidential election.”

Last Friday, an attorney for the Republican National Committee took a similar tack against MoveOn.org by sending a letter to TV stations ominously warning that, as broadcasters, “you have the responsibility to the viewing public … to refrain from complicity in any illegal activity.” All the stations ran the ad anyway.

The watchdogs at the Federal Election Commission tend to move slowly, so these ads can probably air for months without a rebuke.