WASHINGTON – Can Sen. Olympia J. Snowe wait until September? Can Rep. Dan Boren?

In the congressional battle over the war, these two moderates represent the Iraq debate’s fragile center, a confluence of conscience and political calculation where the fate of U.S. policy may be determined over the next three months.

Prominent Republicans in Congress already are abandoning President Bush, as they sense that he is clinging to a lost cause in Iraq. Facing pressure from anti-war liberals, Democrats this week will renew their quest to bring U.S. troops home as quickly as possible. The White House hopes to maintain the status quo until military officials deliver a highly anticipated progress report after Labor Day.

As that charged debate unfolds, The Washington Post will follow four lawmakers whose struggles to come to terms with the conflict will help shape the congressional outcome. Snowe, R-Maine, last visited Iraq in May and thought it looked like Berlin at the end of World War II. Struggling for the right answers, Boren, D-Okla., listens carefully to his conservative constituents and consults regularly with his father, former Sen. David L. Boren, who chaired the intelligence committee. “He’s one of my best advisers,” the congressman said.

Sen. Johnny Isakson, R-Ga., is wary about the Iraqi government but invokes the smell of jet fuel from the Pentagon fire on Sept. 11, 2001, when he warns of the consequences if the United States leaves Iraq precipitously. Rep. Jan Schakowsky, D-Ill., an anti-war activist, is torn between her desire to bring about the quickest possible end and new pressures, as a member of the House leadership, to be a team player for Speaker Nancy Pelosi, D-Calif.

Snowe gave up on the war a year ago but so far has rejected Democratic deadlines for troop withdrawals. In Boren’s mind, he isn’t qualified to dictate war policy to the commander in chief. So far, Isakson is willing to wait for the September report. But like most Republicans, he expects the Iraqi government to deliver on at least some of the benchmarks for progress that Congress established in May.

Bush so needs the support of pro-military lawmakers such as Boren that the White House has established a dedicated liaison for the Oklahoma Democrat, complete with a private phone number. Whatever Isakson’s concerns, he thinks Pelosi and Senate Majority Leader Harry M. Reid, D-Nev., gravely miscalculated when they targeted war funding legislation for fights over troop withdrawal. He recounted one e-mail from a soldier during the heat of the debate: “Please tell the Democrats, I AM the damn war.”

Legislative consensus may be difficult to find in the short term. Bush’s allies number about 35 in the Senate and 180 in the House, compared with a liberal bloc of 29 senators and 169 House members who are demanding that troops come home now.

If there’s a wild card, it is the voices that lawmakers hear on the other end of the telephone when they call to offer condolences to military families. When Sen. Pete V. Domenici, N.M., announced his defection on Iraq last week, the stalwart Republican and former war supporter cited a distinct change in tone that he had detected in recent conversations with family members of casualties.

Snowe recounted the recent death of a Maine soldier, a young man serving his second Iraq deployment. “Every time you talk to a family,” she said, “you have to always think through your policies, your rationale and your purpose.”