Payton, 27, faces a challenge from candidate Guy D. Lewis, 53, a registered nurse and Army reservist from the 179th District, which includes Frankford, Northwood, Oxford Circle, Olney, Feltonville and Hunting Park.

Payton benefited in 2006 when his two competitors were knocked off the ballot. He then weathered a furious write-in campaign for party-endorsed candidate Emilio Vasquez, but his 19-vote margin held all the way to the state Supreme Court.

This year, Payton narrowly survived a challenge to his nominating petitions from Lewis, who is backed by ward leaders Margaret Tartaglione and Dan Savage, and whose Web site features a photo of him with U.S. Rep. Bob Brady, chairman of the Democratic City Committee.

Payton, a former housing counselor, has picked up his own big-name support, including Gov. Rendell, Mayor Nutter, and State Rep. Dwight Evans (D., Phila.)

Blackwell, seeking his third term in the 190th District, did not survive a petition challenge from Vanessa L. Brown. Only Brown will appear on the ballot. The district includes parts of West and North Philadelphia.

Write-in campaigns are notoriously difficult to win, but the Democratic City Committee has offered to help Blackwell with the same kind of campaign that nearly defeated Payton in 2006. In that election, rubber stamps with challenger Emilio Vasquez's name were handed out to voters, making it easy to stamp paper ballots. Blackwell said yesterday that he had at least six stamps to hand out in each of the 72 divisions in his district.

Blackwell, first elected in 2005, is the son of the late U.S. Rep. Lucien E. Blackwell and stepson of City Councilwoman Jannie L. Blackwell.

Brown, a community organizer for the West Philadelphia Coalition, is the niece of Willie Johnson, a prominent businessman and ally of former Mayor John F. Street.

The contest in the 184th District, where incumbent William Keller is challenged by lawyer Christian DiCicco, is an extension of the unending political war between State Sen. Vincent J. Fumo (D., Phila.) and electricians union chief John J. Dougherty.

Dougherty is now the front-runner in the race to succeed Fumo, who faces trial on federal corruption charges in the fall and will not run. He is opposed by Larry Farnese and Anne Dicker.

Keller, a Dougherty ally, has held his South Philadelphia district for 15 years. DiCicco, his challenger, is a lawyer, a former Fumo aide, and son of City Councilman Frank DiCicco.

All told, seven of the 29 House Districts are officially contested in the Democratic primary, with Blackwell's write-in campaign making eight. There are no contested Republican races for the House or Senate.

The races are:

172d District (Northeast): There is no incumbent for Democrats in the 172d House District, where powerful Republican John Perzel, former House speaker, has been entrenched for 30 years. Former Philadelphia Fraternal Order of Police president Richard Costello and Tim Kearney, former aide to the late Councilman David Cohen, are battling for the Democratic nomination to go against Perzel in November.

180th District (North Philadelphia, West Kensington, Hunting Park): Incumbent Democrat Angel Cruz, a member of the House since 2001, takes on challenger Jonathan Ramos, a retired Philadelphia police officer.

182d (Grays Ferry, Center City, South Philadelphia): Incumbent Babette Josephs is challenged by electricians union member Robert J. Gormley Jr. and community activist Peggy Banaszek.

186th (Point Breeze, Southwest): Incumbent Harold James, a former Philadelphia police officer, has been in office since 1989. Challenger Kenyatta Johnson has worked as an aide to Sen. Anthony Williams and founded the "Peace Not Guns" youth conflict-resolution organization.

198th (Chestnut Hill, Mount Airy, Germantown, East Falls, Nicetown and Logan): Rosita C. Youngblood, a 14-year veteran of the House, faces Byron Davis, a teacher at Germantown Friends School.