Senior Democrats have vowed to fight Barack Obama’s new plan for what they call a “carte blanche” expansion of military authority, claiming that proposals presented to Congress on Wednesday do almost nothing to constrain the White House’s ability wage war without approval.

The California congressman Adam Schiff and Virginia senator Tim Kaine singled out the lack of any geographic limits in the proposed three-year authorisation for military force (AUMF) – as well as the failure to repeal a 2001 law previously used to justify attacks – as areas of major concern.

Even as Obama said he was not interested in “perpetual” or “endless war”, leaders of his own party threatened to team up with “strange bedfellows” from the Republican opposition to combat sweeping future presidential power.

In a press conference on Capitol Hill after the White House released its draft legislation to combat the Islamic State, the Democratic leaders ridiculed what they called “broad and vague” language permitting the deployment of US troops in broad circumstances so long as military operations did not involve “a long-term, large-scale ground combat operation”.

“As a practical matter, a president could decide to surge 100,000 troops into Syria for 18 months and claim this is not ‘enduring’,” said Schiff. “It doesn’t put much constraint on the administration.”

“None of us really know what enduring offensive combat operations means; it’s deliberately drafted to be ambiguous,” he added.

In an address from the White House to announce his proposal, the president insisted it was important to keep his options open.

“This resolution strikes the necessary balance by giving us the flexibility we need for unforeseen circumstances,” said Obama.

But he stressed the restrictions on “long-term” ground combat operations and denied that US troops in Iraq were acting in a combat role already; he said they were meant to train allied forces.

“I want to be very clear about what it does or doesn’t do,” the president of his proposed legislation. “It is not authorising another ground war.”

“I do not believe that America’s interests are served by endless war or by remaining on a perpetual war-footing,” he added.

The top Democrats, though, argued there was nothing in the language to stop a future president from launching wars while relying on broad definitions of executive power granted by Congress after 9/11.

“There is a very significant omission from this draft: there is no statute of limitations on the original 2001 authorisation and I think that’s a key problem because, in the absence of that, then when the new authorisation expires three years from now the next president can simply fall back on the old 2001 authorisation and in that respect the new sunset date will have very little impact,” Schiff told reporters.

“I know that’s not the administration’s intention – their intention is that this should serve not to broaden its authority but as a limiting force – but the reality is without a sunset on the old authorisation, it doesn’t limit this administration or the next in any appreciable manner and that’s a key issue in the Democratic caucus in the House judging from the conversation we all had this morning.”

The prospect of these critics being able to tighten the language and limit the authority of Obama and future occupants of the White House, however, remains uncertain.

Many Republicans argue the opposite: by ruling out long-term ground wars, they argue, the White House is severely constraining the military.

“If we are going to defeat this enemy, we need a comprehensive military strategy and a robust authorisation, not one that limits our options,” the House speaker, John Boehner, said in a statement.

Obama said he was “optimistic that it can win strong and bipartisan support” but saw weeks of negotiation ahead to refine the language.

Senator Kaine, a member of the armed services committee, and Schiff, the ranking member on the House intelligence committee, hope to challenge the language in upcoming hearings by linking up with Republican critics.

“There are going to be some very strange bedfellows on this,” said Schiff. “I think there are a substantial number of more libertarian-orientated Republicans who are going to be uncomfortable with a broad authorisation.”

But Schiff acknowledged that most Republican critics wanted looser language for military operations – not just more constraining guidelines for the presidency.

“I find it ironic that some of the same House and Senate members who criticise the imperial president are willing to make him one when it comes to war-making; they are happy to give the president carte blanche,” he added.

Both Democrats welcomed the White House decision to finally seek some congressional approval at least.

“Six-plus months into a war against Isil [as Isis is sometimes known], after thousands of air strikes,” Kaine said, “finally we are at the point where Congress is going to take seriously its most solemn obligation.”

He said he was “mystified it has taken us so long”, but added “this is not the first time this has happened. Whether it is Democrats or Republicans, Whigs or Federalists, we seem to allow presidents to overreach and Congresses to abdicate [responsibility].”