TAIPEI, March 12 (Reuters) - Taiwan's three main

political parties agreed on Thursday to authorise its government

to sign U.S. agreements for four arms sales packages, after

officials warned that Taipei would go to the back of the line if

it missed the deadline.

The back and forth on Taiwan's defence spending has provoked

concern in the United States, as it is the most important

international backer and arms supplier of the Chinese-claimed

island, despite a lack of formal diplomatic ties.

President Lai Ching-te's government has tried to get

parliament to pass $40 billion in extra defence spending but the

opposition, which controls the most seats, says the proposals

are unclear, and it cannot be expected to pass "blank cheques"

despite supporting defence.

Both opposition parties have come up with their own, less

expensive proposals, but the defence ministry has said the

letters of offer and acceptance for the weapons with the United

States have to be signed or Taiwan would lose its place in the

production and delivery queue.

Lawmakers from both sides agreed during a meeting of

parliament's foreign affairs and defence committee that the

government can still sign the agreements in advance, even if the

reviews of the spending proposals are not approved in time.

The weapons to be signed for include TOW anti-tank missiles,

M109A7 self-propelled howitzers, Lockheed Martin ( LMT )-made

Javelin missiles and the HIMARS multiple launch rocket system.

On Tuesday, Defence Minister Wellington Koo told reporters

the HIMARS letter expired on March 26, for 82 systems the U.S.

announced as part of an $11-billion arms sale package for

Taiwan.

Sunday is the deadline to sign for the other weapons

systems, the ministry says.

Last month, a bipartisan group of 37 U.S. lawmakers voiced

concern to senior Taiwan lawmakers about the stalled plans.

The Trump administration has pressed allies to increase

defence spending, a plank Lai and his government have

enthusiastically embraced.