TAIPEI, March 13 (Reuters) - Taiwan's parliament on

Friday authorised the 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.

After lawmakers from both sides agreed on Thursday that the

government could still sign the agreements in advance, even if

the reviews of the spending proposals are not approved in time,

parliament formally gave its legal authorisation.

The authorisation was passed unanimously and announced by

parliament speaker Han Kuo-yu.

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 letters of offer and acceptance for 82 HIMARS systems the

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

Taiwan would expire on March 26.

Sunday is the deadline to sign for the other weapons

systems, the ministry says.

The Trump administration has pressed allies to increase

defence spending, a plank Lai and his government have

enthusiastically embraced.

(Reporting by Ben Blanchard and Roger Tung; Editing by Lincoln

Feast.)