Bipartisan Senate legislation introduced on Wednesday aims to change the administration’s course on nuclear arms control, urging Donald Trump to extend the New Start treaty with Russia or provide justification for allowing it to expire.

Trump has already pulled out of the 2015 nuclear deal with Iran and the Intermediate-range Nuclear Forces (INF) treaty with Russia, which is due to end on Friday.

That would leave New Start, which limits strategic nuclear warheads deployed by the US and Russia to 1,550 each, as the last formal restraint on the world’s major arsenals and its demise is widely seen as the potential death of arms control.

Trump has been dismissive of the treaty, signed by his predecessor, Barack Obama, in 2010. The national security advisor, John Bolton, said it was “unlikely to be extended” when it expires in February 2021.

“Why extend the flawed system just to say you have a treaty?” Bolton asked rhetorically at a rally of young conservatives on Tuesday.

New legislation introduced on Wednesday by Democratic Senator Chris Van Hollen, and Republican Senator Todd Young, seeks to insert Congress into nuclear decision-making as a counterweight to hawks like Bolton.

The bill, seen by the Guardian, calls for New Start to be extended until 2026 unless Russia can be shown to be in material breach of the treaty, or a new agreement is signed which “provides equal or greater constraints, transparency, and verification measures”.

The administration has insisted it is conducting an inter-agency review of New Start, but arms control advocates fear that Bolton and other hawks are running out the clock on the treaty, with no intention of extending or replacing it.

Trump has expressed interest in pursuing a new arms control agreement but one that includes China.

“I think we are going to end up making a deal with Russia where we have some kind of arms control because all we are doing is adding on to what we don’t need and they are too. And China is trying to catch us both,” Trump told C-Span on Tuesday.

As the Chinese arsenal is believed to be a twentieth of the size of Russia or the US, and is not operationally deployed (warheads are stored separately from missiles), administration critics believe the inclusion of China, is a “poison pill”, included with the intention of preventing substantive negotiation before New Start expires. Beijing has said it has no interest in such a deal.

The new Senate legislation, which mirrors a similar bill in the House of Representatives, imposes reporting requirements on the administration with the aim of forcing it to justify its rationale for allowing New Start to expire.

Within six months of the bill being passed, the director of national intelligence (DNI), will have to provide assessments to Congress on the projected Russian arsenal, with and without a New Start extension.

The value and accuracy of such assessments is in doubt since Trump fired the incumbent DNI, Dan Coats, who is generally seen as providing unvarnished summaries of the analysis of the intelligence agencies. In his place, the president has nominated a congressman, John Ratcliffe, who is a Trump ultra-loyalist.

It is unclear whether Ratcliffe will be confirmed by the Senate. Former intelligence officers have said they fear that if he gets the job he will shape assessments to conform to what Trump wants to hear.

The new DNI would have to testify over how the intelligence community’s confidence in its estimates of Russia’s nuclear forces would be affected by the expiration of the treaty, which provides for extensive and frequent mutual inspections and exchanges of information. It also requires an assessment of the intelligence effort needed to make up for the treaty lapsing.

The intelligence agencies would also have to give an assessment of the scale of Chinese nuclear forces. And the secretary of state would have to tell Congress about the efforts to negotiate with Moscow, and any extension offers from either side.

“Now more than ever we must preserve effective, verifiable limits on Russia’s nuclear arsenal,” Senator Van Hollen said. “The New Start treaty has succeeded in doing that over the last nine years and abandoning it would undercut national security and the security of our allies.”

Senator Young said: “This treaty is set to expire in 2021, and as renewing this treaty is debated, we must approach the decision with our eyes wide open to how the threats from nuclear weapons have evolved since the first New Start.”

“Significantly, these two new senators - elected to first terms in 2016 - are making a significant statement that bipartisan support exists for continuing robust arms control such as the new start treaty while thinking ahead to future arms control priorities,” Pranay Vaddi, a former state department arms control official now at the Carnegie Endowment for International Peace.

Thomas Moore, a former senior advisor to the Senate foreign relations committee, called the bill “a big deal”.

“It shows that everyone is not in lock step with the end of arms control,” Moore said. “And it shows at least one Republican thinks we need better answers on New Start’s end.”