By ED JOHNSON
Associated Press Writer

LONDON (AP)_ Prime Minister Tony Blair said Tuesday he would put a new European Union constitution to a nationwide vote, bowing to demands from opposition Conservatives who say the new charter would threaten British sovereignty.

The move confirmed an abrupt reversal of Blair's adamant opposition to such a vote, for which no date was set. It would likely not be held until after the next British general election in 2005.

Blair said the referendum question would be on the constitution, ``but the implications go far wider.''

``It is time to resolve once and for all whether this country, Britain, wants to be at the center and heart of European decision-making or not; time to decide whether our destiny lies as a leading partner and ally of Europe, or on its margins,'' Blair said in the House of Commons.

Blair's about-face, the most significant since he came to power in 1997, follows months of pressure by the main opposition Conservative Party, which claims the treaty will undermine Britain's sovereignty.

Several national newspapers have also taken up the call for a referendum. ``Blair's EU humiliation,'' the Daily Mail's front page headline said Tuesday.

The government had argued against a national poll, insisting that the constitution, which aims to streamline decision making in the EU, would not fundamentally alter Britain's relationship with the bloc.

The reversal in allowing the first nationwide poll since 1975 is a sign that Blair's authority has eroded. Since the Iraq war, Blair's personal ratings have slumped and he is struggling to regain public trust.

Blair said he hoped the constitution could be concluded on schedule in June.

The reversal in allowing the first nationwide referendum since 1975 is a sign that Blair's authority has eroded. Since the Iraq war, Blair's personal ratings have slumped and he is struggling to regain public trust.

``It is a sign of weakness,'' said John Curtice, professor of politics at Strathclyde University, who noted the government had failed to successfully argue its pro-European agenda.

Opinion polls find that many Britons are ambivalent or skeptical about closer European integration, fearing the constitution will create a European super state, and a referendum on the issue is likely to be tight.

Denmark, Ireland and Luxembourg have already announced they will hold referendums on the constitution and several other countries, including the Netherlands, Poland, Italy, Spain and Portugal are likely to do so.

In order for the constitution to come into force, all 25 states must ratify it.

Any referendum would be unlikely before national elections, expected in May 2005.

The largely Euroskeptic Conservatives say a constitution would undermine the country's powers over criminal justice, taxes and foreign policy. The party is making the referendum a central plank of its campaign for European elections on June 10.

Voters traditionally use European elections to vent their grievances about the party in power. A shift in government policy could defuse the referendum issue as one possible liability for the government.

``It is about buying time, trying to take Europe out of the agenda,'' said Curtice.

Blair's government has held several regional referendums, on issues such as devolved government and directly elected mayors.

A referendum on the constitution would be the first nationwide poll since 1975, when Labour Prime Minister Harold Wilson consulted the public on Britain's continued membership in what was then the European Common Market.

That referendum endorsed Britain's membership with a 67 percent ``yes'' vote on a 65 percent turnout.

AP-NY-04-20-04 0903EDT