IF YOU CARE ABOUT politics, you should know there's another presidential debate tonight.

If you care about truth, you should know about FactCheck.org.

The debate is at 9 p.m. It's Democrats at Dartmouth College, in New Hampshire, moderated by NBC's Tim Russert, broadcast live on MSNBC-TV.

FactCheck is a watchdog group doing what more media should be doing - holding all candidates accountable for everything they say.

The non-partisan, non-profit group accepts no money from corporations, political parties, labor unions, lobbyists or individuals.

It's funded by the Annenberg Public Policy Center at Penn and is gaining in popularity; my guess is because too much mainstream media is too busy chasing O.J., Brittany and Lindsay Lohan.

FactCheck monitors political ads in the top 100 media markets, pointing out exaggerations and inaccuracies; and it follows presidential debates, noting (usually the next day) any attempts to fool even some of the people some of the time.

You can subscribe to FactCheck's free service to get alerts, summaries and special reports sent directly to your e-mail box.

It is, especially given the large presidential field, an invaluable service.

"This is the core job of a free press," says director Brooks Jackson, a former Associated Press, Wall Street Journal and CNN national reporter.

"My ultimate goal," he tells me, "is to be not needed."

For now, however, FactCheck's staff of seven works out of the National Press Building in Washington, busily, well, checking facts.

For example?

* In May, at the first GOP debate, at the Reagan Library in California, Rudy Giuliani said adoptions in New York City went up 73 percent when he was mayor - a sensitive issue for a GOP pro-choice candidate.

Problem is while the rate jumped before he was mayor and climbed during some of the time he was mayor, the overall rate of increase during his tenure was 17 percent.

* In August, at the AFL-CIO debate in Chicago, Democratic Sen. Joe Biden boldly claimed no other candidate on the stage "has a better labor record than me."

Turns out every other candidate on the stage had a better record - as reflected in AFL-CIO lifetime ratings.

* Also in August, at a candidate forum on cancer issues in Iowa, Hillary Clinton said 500,000 women die annually from cervical cancer.

While calling Clinton "a human encyclopedia" with facts and figures, FactCheck said this time she was wrong.

The National Cancer Institute says there are 500,000 diagnosed cases of cervical cancer annually; the worldwide fatality number is 250,000.

* FactCheck also notes New Mexico Gov. Bill Richardson keeps insisting that U.S. school kids used to rank first in world in math and science and now rank 29th. Neither is true.

* Former Massachusetts Gov. Mitt Romney said in August "if you look at lists compiled on Web sites," you find New York at "the top of the list" of sanctuary cities for illegal immigrants at the time Giuliani was mayor.

FactCheck could find no such lists but said three Massachusetts cities, Cambridge, Orleans and Somerville, were sanctuary cities during Romney's tenure.

All FactCheck work includes all sources and related articles.

And while it started back in '03, FactCheck is now really starting to pick up steam. It has 66,000 subscribers. Visits to its Web site doubled since April, running above half-a-million a-month.

There are plans to add a Q&A section to the site, a mobile version for personal digital assistants like BlackBerry and maybe a broadcast element.

And even if it doesn't force politicians to mend their ways ("If I were to hope for that, I'd be perpetually disappointed," says Jackson), it clearly represents a boon for voters, students of politics and those who seek the truth. *

Send e-mail to baerj@phillynews.com.

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