WASHINGTON -- Ever since President Bush announced his intention to restructure the Social Security system, some congressional Republicans have worried they would suffer negative political fallout back in their districts -- particularly when the debate turned to potential benefit cuts and the creation of private accounts for younger workers.

MoveOn.org, a 3 million-member liberal grassroots group, is wasting no time in trying to bring those worries to fruition.

Today in New York, Washington and three congressional districts -- including Pennsylvania's 6th District -- the group will begin airing TV ads that show elderly people mopping factory floors, moving heavy boxes and shoveling building materials into a Dumpster. An announcer says Americans will need to get used to "working retirements," and the ads criticize what MoveOn describes as the president's proposal to cut Social Security benefits to pay for private accounts.

The Pennsylvania version then urges viewers to contact U.S. Rep. Jim Gerlach, R-Upper Uwchlan Township, Chester County, to pressure him to oppose the Bush plan.

Gerlach's spokeman, John Gentzel, yesterday said the congressman has not taken a position on any of the possible proposals leaking out of the White House, but added that Gerlach generally opposes the privatization of Social Security.

So far, Bush has released only broad outlines of his approach to Social Security, the centerpiece of which is to allow younger workers to divert payroll taxes to private investment accounts. He is expected to provide more details in his State of the Union address tomorrow evening.

Tom Matzzie, Washington director of MoveOn, said the ads are just the beginning of a broad effort to pressure members of Congress to fend off the president's plans.

Matzzie said the fact that Gerlach won his seat in 2002 and 2004 by just a 2 percentage-point margin, made him a more likely target to oppose the President's Social Security plan.

Residents of Western Pennsylvania could start seeing similar ads soon. Matzzie said Pennsylvania's Reps. Melissa Hart, R-Bradford Woods, and Tim Murphy, R-Upper St. Clair, are both on MoveOn's "watch list" of potential congressional targets because they represent districts with aging populations and a large number of Democrats.

Aides to Hart and Murphy yesterday said their bosses were still in the "fact-finding phase" regarding Social Security. Murphy's press secretary, Mark Carpenter, said Murphy opposes raising the retirement age, increasing payroll taxes or cutting benefits, but that he is waiting to hear more details of the president's plan.

The two other members of Congress targeted in MoveOn's first round of ads are Reps. Allen Boyd, D-Fla., who has said he supports creating private accounts, and Chris Chocola, R-Ind., who represents another closely divided district.

Matzzie said the ad buy was substantial and that his group today will launch a campaign to raise at least a half-million dollars to pay for it.