Two senior Democratic lawmakers with central roles on defense issues are stepping up their pressure on President Obama to resist Pentagon recommendations for a troop surge in Afghanistan.

Michigan Sen. Carl Levin , chairman of the Senate Armed Services Committee, and Pennsylvania Rep. John P. Murtha , chairman of the House Defense Appropriations Subcommittee, each drew parallels between the president’s coming decision and past presidential decisions that led to two U.S. strategic military debacles: the Bay of Pigs and Vietnam.

Murtha also raised concerns about dire economic risks of expanding the war in Afghanistan, where he said there is no apparent “achievable goal.”

Obama is considering a course of action in Afghanistan that could include a deployment of up to 40,000 more U.S. troops, on top of the existing troop commitment of 68,000, a total that will be reached by the end of November.

He is considering this troop surge in the wake of the bloodiest month to date in the 8-year-old Afghanistan war. In October to date 55 Americans have died and about 276 have died there this year.

In a speech at a Rand Corp.-sponsored event on Afghanistan policy, Levin called for a U.S. approach based on a model recently outlined by British Prime Minister Gordon Brown that “demonstrates renewed resolve, by dedicating significant new resources, by committing to the counter-insurgency strategy and by demonstrating enhanced capability, while at the same time minimizing the perception of a foreign occupation.”

Levin explained that the plan would begin with “a major, publicly delivered commitment to intensified training, mentoring of and partnering with Afghan forces,” and includes providing new equipment, an increase in flights of unmanned aerial vehicles, and additional funding.

It also would include a small force commitment of about 9,500 troops and be contingent upon “major” commitments from the Afghan government, including a massive expansion of its military and security forces. The action, Levin said, also is contingent upon NATO support.