Under the "Let down by Labour" banner, the winning ads will be used as part of its advertising campaign for the crucial local and European elections in June.
Successful posters and 30-second films will feature on billboards and in the Party's election broadcasts alongside work developed by the party's advertising agencies M&C Saatchi and VCCP.
The best will also appear on a new website .
The competition follows the example of , the US liberal anti-war group that held a competition to create a 30-second commercial attacking George W Bush and has been supported by celebrities including Martin Sheen and Michael Stipe.
Conservative Party chairman Liam Fox said the idea gave the public a chance to be involved in real politics and not political cliches.
"The public are looking for authenticity in politics, not political cliche. You can just imagine how proud the successful people will feel when they see their ideas put into action," he said.
The latest initiative is the work of the former O2 marketer Will Harris, who joined the Tory Party as marketing director in November and reports to joint party chairman Lord Saatchi.
The June elections are being seen as a crucial tester in the run-up to a possible general election in 2005 as Tony Blair's popularity is at its lowest ebb following the invasion of Iraq and the Hutton Report.
"The British people feel greatly let down by Labour. That is why the June elections provide people with an opportunity to send this government a message," Fox said.
Fox added that the idea put the Tories back at the forefront of political advertising, harking back to the Saatchi & Saatchi-created "Labour isn't working" creative.
"The Conservative Party has always been at the forefront of developments in political campaigning and advertising -- from the famous 'Labour isn't working' campaign that propelled Margaret Thatcher to power to the 'Tax bombshell' campaign that contributed to John Major winning," Fox said.
The Tories most recent advertising effort was a spoof of the Linda Barker's DFS sofas ads attacking Gordon Brown whom the party calls the "credit card" Chancellor.
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