SAN FRANCISCO — Pillsbury Winthrop Shaw Pittman laid off 55 lawyers and 100 staff on Thursday, finalizing a move revealed by an indiscreet partner on an Amtrak train last month.

The cuts include associates and counsel from across the country, accounting for a 12 percent reduction in Pillsbury’s nonpartner ranks.

“As previously announced, Pillsbury, like many of its fellow law firms, has found it necessary to implement a workforce reduction in order to bring our resources in line with client demand,” the firm said in a prepared statement.

It had been previously announced because a tipster to legal blog Above the Law heard a D.C.-based Pillsbury partner loudly discussing the impending cuts on his cell phone while riding the train. Then, last week Pillsbury offered voluntary buyouts to associates and staff. Pillsbury said that some took the deal, but declined to say how many.

The firm is giving laid-off attorneys three months’ severance, while packages for staff will be based on seniority. The firm also is offering a unique alternative to the severance: It’ll fund one year of salary and benefits, on the nonprofit pay scale, for laid-off lawyers who go to work at legal nonprofits.

“We believe that associates can strongly benefit from this opportunity to enhance their legal skills and obtain additional professional experience while helping to meet the needs of their respective communities in this very difficult time,” the firm said in a statement.

Bingham McCutchen also announced it was cutting 16 corporate lawyers and 23 staff Thursday. A firm spokeswoman said that no Bay Area lawyers were affected, but two from Los Angeles and Orange County were let go.

Bingham has been cutting staff over the past year. Last month, the firm cut seven staff when it shut down its Walnut Creek office. Last May, the firm cut 17 staff from its San Francisco and Silicon Valley offices.

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Only a few big firms with major presences in the Bay Area haven’t resorted to layoffs. Morgan, Lewis & Bockius, which counts more than 200 local lawyers, hasn’t announced reductions; a firm spokeswoman didn’t return a call seeking comment on Thursday. Jones Day, which has about 150 lawyers in the Bay Area, also has not laid off attorneys.

“Jones Day has not laid off lawyers and staff and does not plan to do so,” the firm said in a statement.

Pillsbury becomes the last of the major Bay Area-based firms to make major cuts. Orrick, Herrington & Sutcliffe even conducted a second round this week, cutting 300 lawyers and staff. It had previously cut 75. Recorder affiliate The Am Law Daily reported on Thursday that West Coast firms have cut more than their East Coast counterparts so far.

Pillsbury saw slight dips in revenue and profits last year, bringing its profits per partner to $975,000. The firm had 823 lawyers before the cuts. With the cuts, the firm now has 366 partners and 402 nonpartners — nearly a one-to-one ratio.

Pillsbury downsized its staff and lawyers in 2008, but never disclosed exactly how many it cut. Earlier this year, Chairman James Rishwain Jr. said the firm had reduced costs dramatically, explaining that some of those 2008 reductions were voluntary, some were performance-based and some were based on excess capacity.

The layoffs have reached a fever pitch in the Bay Area. One local partner at a firm that hasn’t done layoffs said that law firm chiefs need to look in the mirror before making cuts.

“The hard question that these guys should answer is why they’re putting longtime associates and staff out on the street in these difficult economic times rather than taking home a hundred thousand less in their own paychecks,” he said. “It looks like the partners are more loyal to themselves than the associates and staff they depend on.”