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* UK needs to replace subs carrying nuclear weapons by 2030s
* Opposition Labour leader and some lawmakers oppose renewal
* Ministry of Defence estimates replacement cost at 31 blnpounds (Updates after vote)
By Michael Holden and Kylie MacLellan
LONDON, July 18 (Reuters) - Lawmakers voted strongly onMonday to renew Britain's ageing nuclear weapons system, amultibillion-pound project regarded as key to maintaining thecountry's status as a world power following its vote to leavethe European Union.
Despite opposition from the pro-independence ScottishNational Party (SNP) and some in the opposition Labour Party,parliament approved the renewal of the Scottish-basednuclear-armed Trident submarines by 472 to 117 votes.
Some opponents said the vote was being used by new PrimeMinister Theresa May to unify her party, which has aparliamentary majority of 16, after a bruising Brexit campaign,and embarrass Labour by highlighting its own deep divisions.
In her first statement in parliament as prime minister, Mayurged lawmakers to back Trident, not only to protect Britainfrom growing threats from Russia and North Korea, but also toprotect thousands of jobs in Scotland and elsewhere.
"What this country needs to do is to recognise that it facesa variety of threats and to ensure we have the capabilities thatare necessary and appropriate to deal with each of thosethreats," she said ahead of the vote.
Britain needed to retain a nuclear deterrent which had beenan insurance policy for nearly 50 years, May said.
"We cannot outsource the grave responsibility we shoulderfor keeping our people safe ... That would be a reckless gamble:a gamble that would enfeeble our allies and embolden ourenemies; a gamble with the safety and security of families inBritain that we must never be prepared to take."
Parliament agreed in principle in 2007 to replace thedeterrent system and Monday's vote was to rubber stamp thedecision to approve the building of four submarines to ensureBritain can have nuclear weapons continuously on patrol at sea.
UK'S "OUTSIZED" ROLE
U.S. Defence Secretary Ash Carter said in February Britainmust renew the submarines, based at Faslane, if it wanted tomaintain its "outsized" role in world affairs.
During more than five hours of debate in parliament, manyargued that failing to renew the system would mark Britainretreating from the world.
However, Scottish nationalists and some in Labour believethe weapons are no longer needed as they are little use againstterrorists and the money could be better spent elsewhere.
Labour leader Jeremy Corbyn, who has been challenged by twocandidates seeking to take the helm of the centre-left party,questioned the need for Britain to possess "weapons of massdestruction" and said it should press for a nuclear-free world.
"I would not take a decision that kills millions of people,I do not believe the threat of mass murder is a legitimate wayto go about dealing with international relations," said Corbyn,who had indicated his lawmakers could vote freely on Trident.
Many Labour lawmakers criticised their leader's view, whichis in contrast with the party's official position on Trident.
SNP Westminster leader Angus Robertson said the renewal wasopposed by Scotland, where May's Conservatives hold just one ofthe 59 seats in the British parliament.
"It is obscene that the priority of this government ... isto spend billions of pounds on outdated nuclear weapons that wedo not want, do not need and could never use," he said duringthe debate.
"This government has a democratic deficit in Scotland andwith today's vote on Trident it is going to get worse notbetter."
SELF-HARM
Some military officials also oppose the outlay on Trident,saying the money would be better spent on maintaining the armyand on more conventional technology, both of which have recentlysuffered cutbacks.
The Ministry of Defence has said replacing the foursubmarines would cost 31 billion pounds ($41 billion), plus acontingency fund of 10 billion pounds, with another 4 billionalready allocated to the design process.
Defence firms BAE Systems, Rolls-Royce andBabcock can expect to benefit from a renewal, with thenew submarines expected to enter service from 2028.
However, in response to a freedom of information requestfrom Reuters in March, the ministry said it could not providedetails of the costs for the nuclear warheads, support servicesinfrastructure and running costs over the system's expectedlife.
Calculations by Reuters and Conservative lawmaker CrispinBlunt suggest it could reach 167 billion pounds ($220 billion)over 32 years.
Blunt, head of the parliament's foreign affairs committee,said on Monday the costs had increased and may eventually reach180 billion pounds.
"I oppose the renewal of Trident because I care about thesecurity of my country," he said in a statement. "I'm notprepared to be party to the most egregious act of self-harm toour conventional defence." ($1 = 0.7583 pounds) (Additional reporting by Elizabeth Piper and Sarah Young;Editing by Giles Elgood and James Dalgleish)