A treaty to ease the supply of military equipment from the US to UK forces must not be "blunted" by over-restrictive regulations, MPs have said.
The deal is intended to make it easier for troops to get equipment
The Defence Trade Co-operation Treaty, signed earlier this year, removes the need for licences for some arms sales and sharing of technology research.
The Commons defence select committee said small firms in the UK should not be excluded from the changes.
It was "vital" not to prevent forces getting access to equipment, it added.
The treaty was signed in June by then prime minister Tony Blair and US President George Bush, but detailed arrangements are still to be negotiated.
The committee said change was essential because the current restrictions on defence exports from the US to the UK were "unduly burdensome and time-consuming".
It added that if rules were too tightly drawn they could "seriously blunt the effectiveness" of the treaty.
The committee stressed that smaller firms and major foreign-owned defence firms in the UK should not be excluded from the deal.
It said: "The US and the UK are very close allies, co-operating closely on defence and security.
"Our soldiers are fighting side by side in Iraq and Afghanistan."
It also said: "It is vital to the interests of both the US and the UK that the system should not prevent our forces from getting access to the equipment they need to fight effectively alongside their US allies in current and future operations."
The treaty has to be ratified by the UK Parliament and the US Congress.
Committee chairman Conservative MP James Arbuthnot said: "The committee is fully behind the principle of this treaty.
"As long as the implementing arrangements do not include a long list of exclusions, it should make a step-change in our defence collaboration with the US - and make a real difference to our troops on the ground."