WASHINGTON — Looking to stake out her own foreign-policy position among Democrats contending for the presidency, Senator Clinton is calling for Congress to impose a cap on troops in Iraq, set conditions for continued economic aid to its government, and increase the number of American forces in Afghanistan.

Mrs. Clinton issued the proposals yesterday in a series of appearances upon returning from a weekend trip to the Middle East. They come as the early — but still undeclared — front-runner for the Democratic presidential nomination is facing increasingly aggressive challenges from across her party, most notably from Senator Obama of Illinois, who created an exploratory committee Tuesday.

The former first lady’s proposals are her most far-reaching yet in pushing for a new policy in Iraq, but they do not go as far as some Democrats who are urging Congress to cut off funding for the war and to set a definite date for the withdrawal of American troops. “I do not support cutting funding for American troops, but I do support cutting funding for Iraqi forces if the Iraqi government does not meet set conditions,” Mrs. Clinton told a packed news conference at the Capitol.

Mrs. Clinton is staunchly opposed to President Bush’s plan to send more than 20,000 additional troops to Iraq, and she pushed for congressional action to restrain him. She said she would introduce a bill that would cap the number of troops at the levels they were at the beginning of this month and require the president to seek approval from lawmakers to increase it.

At the same time, Mrs. Clinton acknowledged that lawmakers would probably do little in the short term, noting that Mr. Bush was already moving forward with his plan and that the votes might not be there in the House and Senate. “I can count,” she said.

Appearing alongside Senator Bayh, a Democrat of Indiana, and Rep. John McHugh, a Republican of upstate New York, Mrs. Clinton also reiterated her previous support for a phased redeployment of troops from Baghdad.

She made her new policy pronouncement as a new Los Angeles Times/Bloomberg poll showed that just one-third of Americans approve of Mr. Bush’s handling of the war and more than half — 51% — said Congress should act to block his planned troop increase. The responses to Mrs. Clinton’s proposals yesterday indicate how much pressure she is facing from all sides as she plots her widely expected run for the White House. While an anti-war group urged Mrs. Clinton to turn “words into action,” the White House called her proposal “a pretty extreme move.”

Shortly before her press conference yesterday, Senators Biden of Delaware and Levin of Michigan, both Democrats, and Senator Hagel of Nebraska, a Republican, announced a bipartisan, nonbinding resolution that said “escalating” the American military presence in Iraq was not in the country’s best interest and that America should transfer, under an “expedited timeline,” responsibility for security to the Iraqis.

Mrs. Clinton said she would vote for the resolution, and later in the day, she released a statement saying she would be a co-sponsor.

While she backed an “expedited timeline,” she would not commit to a specific date by which most troops should be out of Iraq, as have some Democrats, including Senators Edwards and Kerry. “I’m not going to support a specific deadline,” she told reporters.

A day after taking a major step toward running in 2008, Mr. Obama issued a statement in which he chided lawmakers who voted for the Iraq war in 2002, saying “the fact that the president is already moving ahead with this idea is a terrible consequence of the decision to give him the broad, open-ended authority to wage this war in 2002.” Those senators include Mrs. Clinton, as well as other potential 2008 rivals, Senators Edwards and Kerry. Mr. Obama was not in the Senate at the time.

In morning appearances on NBC and CBS, Mrs. Clinton dodged questions about Mr. Obama’s entry into the race and did not say when she would announce her decision.

Also yesterday, the campaign manager for Senator Edwards, David Bonior, sent an e-mail titled “Total Bull” to supporters asking them to sign a petition urging Congress to “block funding for Bush’s escalation of the war.” Mr. Edwards has sought to solidify the anti-war mantle among the major Democratic presidential hopefuls. “If you hear a member of Congress say ‘nonbinding resolution,’ then you’re really hearing them say ‘pass the buck,'” Mr. Bonior wrote.

The anti-war group Moveon.org also upped the ante on Mrs. Clinton yesterday in response to her proposals. “We look forward to seeing Senator Clinton use her powers as a senator to stop the escalation and move towards a redeployment,” the group’s Washington director, Tom Matzzie, said in a statement. “A key test is how the senator puts words into action.” On the other side, the White House press secretary, Tony Snow, said Mrs. Clinton’s proposed cap would “bind the hands” of the commander in chief. “To tie one’s hands in a time of war is a pretty extreme move,” he said at his daily press briefing.

Mrs. Clinton received more support in her call for more troops in Afghanistan. Secretary of Defense Gates said he is considering a request from commanders there for additional forces, the Associated Press reported.