"If the president chooses to escalate the war, in his budget request, we want to see a distinction between what is there to support the troops who are there now," she said in an exclusive interview on Face The Nation.
"The American people and the Congress support those troops. We will not abandon them. But if the president wants to add to this mission, he is going to have to justify it and this is new for him because up until now the Republican Congress has given him a blank check with no oversight, no standards, no conditions," said Pelosi, D-Calif.
Her comments came as Mr. Bush worked to finish his new war plan that could send as many as 20,000 additional U.S. troops to Iraq and provide more money for jobs and reconstruction programs.
Mr. Bush is expected to announce his plan as early as Wednesday.
When asked about the possibility of cutting off funds, House Majority Leader Steny Hoyer declined to say whether Democrats might do so, saying only that the current strategy clearly is "not working."
"I don't want to anticipate that," said Hoyer, on "Fox News Sunday."
Some military officials, familiar with the discussions, say Mr. Bush at first could send 8,000 to 10,000 new troops to Baghdad, and possibly Anbar Province, and leave himself the option of adding more later if security does not improve.
"Based on the advice of current and former military leaders, we believe this tactic would be a serious mistake," Senate Majority Leader Harry Reid said Saturday in the Democratic radio address.
Pelosi and Reid told Mr. Bush in a letter last week that Democrats oppose additional U.S. forces in Iraq and want him to begin withdrawing American troops within four to six months.
Pointing to the November elections that ousted Republicans from control of the House and Senate, Pelosi told Bob Schieffer the public is "watching to see what difference this election can make. The president ought to heed their message... We should not be obliged to an open-ended war."
She said Democrats are not interesting in cutting off money for troops already in Iraq — "We won't do that" — and that her party favors increased the overall size of the Army by 30,000 and Marines by 20,000 "to make sure we are able to protect the American people."
"That's different though, than adding troops to Iraq," Pelosi said.
The speaker stopped short of stating categorically that Democrats would block money for additional troops in Iraq. But she did say, "The burden is on the president to justify any additional resources. ... The president's going to have to engage with Congress in the justification for any additional troops."
Sen. Joe Biden, Democratic chairman of the Senate Foreign Relations Committee, said it would be a "tragic mistake" if Mr. Bush chooses to increase troops. But Biden said cutting off funds was not an option.
"As a practical matter there is no way to say this is going to be stopped," Biden said regarding a troop increase, unless enough congressional Republicans join Democrats in convincing Mr. Bush the strategy is wrong.
Biden added that it probably would be an unconstitutional violation of separation of powers if Democrats were to block Mr. Bush's efforts as commander in chief after Congress had voted to authorize going to war.
"It's unconstitutional to say, you can go, but we're going to micromanage," Biden said.
Although most of the discussion about Mr. Bush's anticipated plan has focused on troop strength, his strategy also is expected to address political and economic issues.
Military analysts say Army Lt. Gen. Peter Chiarelli, who recently finished his tour as the No. 2 general in Iraq, has recommended a short-term jobs program.
Mr. Bush is said to favor short-term jobs programs, making micro-loans to small business and increasing the amount of money that military commanders can spend quickly on local projects to improve the daily lives of Iraqis.
Mr. Bush is expected to continue his briefings with lawmakers this week, culminating in a meeting with bipartisan leadership on Wednesday, according to lawmakers and aides.
Since the attacks of Sept. 11, 2001, Congress has approved about $500 billion for Iraq, Afghanistan and other terrorism-fighting efforts. The White House is working on its largest-ever appeal for more war funds — a record $100 billion, at least. It will be submitted along with the president's Feb. 5 budget.
"This war cost a trillion dollars if it ended now," Pelosi said. "But more important than that, the lives lost, the casualties sustained, the lost reputation in the world, and the damage to our military readiness. For these and other reasons we have to say to the president, in your speech ... we want to see a plan in a new direction because the direction you've been taking us in has not been successful.
"So when the bill comes ... it will receive the harshest scrutiny. What do we really need to protect our troops? What is there for an escalation? What is the justification for that?"