Two more veteran Congressmen announced their retirement plans last week, bringing to 27 the number of House Members who are leaving the chamber voluntarily.

Most of them are Republicans.

Although neither departure is likely to change the political makeup of the House, there could be hard-fought primaries to replace 14-term Rep. Tom Lantos (D-Calif.) and six-term Rep. John Peterson (R-Pa.).

In announcing his retirement last week, Lantos, the chairman of the House Foreign Affairs Committee who turns 80 next month, also disclosed that he has esophageal cancer.

Lantos was diagnosed with cancer during Congress’ last week of business in December, according to his communications director, Lynne Weil. She said Lantos, the only Holocaust survivor ever elected to Congress, is considering a range of treatment options, including radiation and chemotherapy.

In California’s 12th district, the winner of the Democratic primary is assured of victory in the overwhelmingly Democratic, San Francisco-area seat.

Former state Sen. Jackie Speier (D), a popular politician with a long history of service to 12th district constituents, was already preparing to challenge Lantos in the June Democratic primary. His retirement should only fuel her desire to run.

Speier was set to meet with her political team on Friday to discuss her plans in the wake of Lantos’ decision to retire, and she is expected to announce her candidacy later this month.

State Sen. Leland Yee (D), who replaced Speier in the California Senate after Speier was termed out, has acknowledged that he is considering a run for Lantos’ seat, while state Assembly candidates Jerry Hill (D) and Gina Papan (D) also are considered potential candidates for the Lantos seat. Hill is a San Mateo County supervisor; Papan is a Millbrae city councilwoman.

One Democratic insider in California suggested that Yee is the only candidate who could prevent Speier from succeeding Lantos when the 111th Congress convenes in January 2009.

“This race is Speier’s to lose unless a cast of thousands gets in and someone can squeeze out some base — like Yee,” the insider said.

A poll conducted for Speier in November suggests that she could have the inside track in the Democratic primary, as the survey had her well in front of Lantos, a political force in his own right.

Speier has a compelling personal story.

In 1978 she was serving as a staffer for then-Rep. Leo Ryan (D-Calif.) and accompanied him to Guyana in November of that year on a mission to investigate possible human rights abuses at the Peoples Temple compound in Jonestown run by the Rev. Jim Jones. Some of Jones’ followers were Ryan’s constituents.

Ryan was killed when Jones’ followers opened fire on Ryan, Speier and others in the fact-finding delegation as they were boarding a plane to head back to the United States.

Speier was shot five times but survived despite lying on the airport tarmac for 22 hours while waiting for medical help to arrive. She subsequently ran and lost the special election to replace Ryan in Congress but later won a seat on the San Mateo County Board of Supervisors.

She later advanced to the state Legislature, and in 2006 she ran for lieutenant governor, finishing a close second in the Democratic primary to now-Lt. Gov. John Garamendi.

Lantos’ retirement also puts the Foreign Affairs gavel into play in the 111th Congress, although Democratic observers point to Rep. Howard Berman (D-Calif.) as the likely successor.

“A Californian will hang on to the gavel. Anyone hoping for a chairmanship fight will be disappointed,” said one House leadership aide, who asked not to be identified.

A senior Democratic aide, who spoke on the condition of anonymity, confirmed that Berman anticipates he will move into the Democrats’ top slot.

“He’s deeply interested in foreign affairs,” the aide said, noting that Berman, who has served on the panel since his 1982 election, outranks the next lawmaker in line by several years. Rep. Gary Ackerman (D-N.Y.), who chairs the Middle East and South Asia subcommittee, joined the committee in 1985. Ackerman’s office could not be reached by press time Friday.

Although the Democratic Steering and Policy Committee considers a variety of factors in selecting committee chairmen, seniority plays a significant role in those deliberations.

But the aide stressed that Berman is not actively pursuing the gavel. “At this moment we are concerned about [Chairman Lantos] and the ways we can help him, and not about any change.”

A spokeswoman for the Foreign Affairs panel declined to comment.

Meanwhile, Peterson cited health problems in his family as the reason for his retirement.

“Unfortunately, although still young at heart, a few chronic, non-threatening health issues have to be addressed at home, requiring me to devote more time to my family — time and presence which would not be possible if I sought re-election,” Peterson, 69, said in a statement. “This was not an easy decision, and there is never a perfect time to leave public service.”

Peterson has easily won all of his general election campaigns with at least 60 percent of the vote and the large, mostly rural district is considered safe for Republicans. However, no one but Peterson had filed to run and the Feb. 12 state deadline to file is fast approaching.

In the wake of Peterson’s surprising announcement, the candidate most often mentioned for the seat is state Sen. Jake Corman (R), who represents the relatively populous Centre County. Corman said he is seriously considering a bid for the seat, but personal factors — including his three young children — could deter a bid.

“I’m going to sit down with my family the next few days and try to come up with a decision by the end of the weekend,” Corman said on Thursday.

State Rep. Matt Baker (R), who represents the northwest section of the 17-county district, also said he is seriously considering running for the seat. However, Pennsylvania Republican operatives tend to agree that the seat is Corman’s for the taking.

“It really is his seat if he wants it,” said a state Republican operative.

Jennifer Yachnin contributed to this report.