PITTSBURGH — The district attorney for the Pittsburgh area is investigating possible forgery and other irregularities on voter registration forms turned in by a group already being scrutinized for registration problems in other states.

Similar allegations are being investigated by the Delaware County district attorney and the U.S. attorney's office in Philadelphia.

The Pittsburgh-area investigation focuses on fewer than 100 registration forms apparently forged or otherwise illegitimate, such as duplicating the name of someone already registered under another party, said Mike Manko, spokesman for Allegheny County District Attorney Stephen Zappala Jr.

The forms were collected by the Association of Community Organizations for Reform Now, or ACORN, Manko said. The investigation mirrors others throughout the country in which ACORN canvassers allegedly turned in forms with fake Social Security numbers, incorrect birth dates, forged signatures or fake addresses.

Pennsylvania Republican Party chairman Robert Gleason Jr. said ACORN and others submitted nearly 253,000 voter registration forms in Philadelphia this year. Thousands of them have errors, he said. Delaware County officials are also investigating more than 290 registration cards, Gleason said.

Philadelphia's voter registration administrator, Bob Lee, said 57,000 of the 253,000 registration forms were rejected, but that more than 41,000 of those were filled out by people who were already registered.

He acknowledges that some of the other 16,000 rejected voter cards are troubling — in particular about 5,600 that include nonexistent addresses. Others were rejected for being too young or not including a birth date. Others list an incorrect Social Security or driver's license number, which could be simple mistakes or attempts at fraud, Lee said.

"So, there's an issue here," Lee said.

Patricia Hartman, a spokeswoman for federal prosecutors in Philadelphia said she could not comment on whether they are investigating the Philadelphia registrations. Delaware County's DA didn't return calls.

ACORN claims to have registered about 1.3 million voters nationwide this year and is facing similar questions in Nevada, Wisconsin, North Carolina, New Mexico, Michigan, Ohio and Missouri. Officials in Nevada said some bogus registration forms used the names of Dallas Cowboys players.

ACORN's stated mission is to help low-income citizens organize politically. The group describes itself as nonpartisan, though Republicans contend it is aligned with Democrats and the Obama campaign.

ACORN issued a statement claiming to have registered 40,000 southwestern Pennsylvania voters this year, and calling media reports about the national fraud allegations an attempt by "a relatively small group of political operatives ... trying to orchestrate hysteria about 'voter fraud."'

Maryellen Hayden, ACORN's head in Allegheny County, told local reporters on Thursday that eight ACORN workers are targeted in the Pittsburgh-area investigation. She said workers were warned not to fill in the registration cards themselves and that other workers double-check the cards for legitimacy.

Allegheny County elections director Mark Wolosik said the county checks each new registration card and referred some questionable ones to the district attorney.