WASHINGTON – Led by labor unions, interest groups that can urge the public to elect or defeat candidates have poured at least $27 million into the presidential race since Labor Day, with Senator Kerry’s backers outspending President Bush’s by more than 5-to-1.

The efforts range from pro-Kerry hard-hat stickers handed out by the International Union of Painters and Allied Trades PAC to pro-Bush radio ads, paid for by the National Right to Life political action committee, airing in every battleground state. Among the biggest spenders, the United Auto Workers PAC yesterday reported $2.5 million in new spending on pro-Kerry ads.

“There’s a lot more to come in the next week and a half,” said Kent Cooper, co-founder of the nonpartisan Political Money Line campaign-finance tracking service.

PACs are financed with limited contributions from individual donors. Their spending pales in comparison to the tens of millions of dollars that partisan groups collecting unlimited donations from companies, unions, and wealthy activists are devoting to ads and get-out-the-vote operations.

But political action committees wield a powerful privilege the other groups do not: PACs can ask the public to vote for or against a particular candidate, something so-called soft-money groups must stop short of doing. PACs can spend unlimited sums in presidential and congressional races as long as they do so independent of the campaigns their efforts support.

“In the presidential race, I think you’re dealing with two factors. One, they want an impact on the race,” Mr. Cooper said. “But there’s probably a certain percentage of it where there’s egos involved, and they want to show their members they played a role in the race…maybe even more so than changing voters’ minds.”

Pro-Kerry labor union political action committees have spent about $11 million since Labor Day reaching voters both individually and en masse. The spending includes television and radio ads, hats, T-shirts and Frisbees, mass mailings, yard signs, telephone calls, and door-to-door visits.

Environmental PACs are the next highest presidential spenders. Groups including the Sierra Club and the League of Conservation Voters have devoted roughly $4 million in PAC money to efforts supporting Mr. Kerry or opposing Mr. Bush.

On Mr. Bush’s side, the National Rifle Association’s PAC has spent more than $3 million opposing Mr. Kerry or supporting Mr. Bush. Anti-abortion PACs, including National Right to Life’s, also have spent heavily to back Mr. Bush, together pouring in more than $1 million.

Though the presidential race draws most of PACs’ independent spending, high-profile congressional contests that will determine which party controls the House and Senate are also attracting special-interest money.

In all, PACs have devoted roughly $7 million to independent efforts in congressional races since Labor Day, an Associated Press review of reports they filed with the Federal Election Commission shows.