WASHINGTON (AFP) - The rapidly expanding field of 2008 presidential contenders has set off a frenzied battle for all-important campaign donations, as the money-driven US election contest gathers steam.

The 2004 presidential election broke spending records, but the current campaign is expected to eclipse that one, according to federal election officials.

"The 2008 race will be the longest and most expensive election in American history," former Federal Election Commission chairman Michael Toner told reporters recently.

Toner said campaign spending would likely approach the one billion dollar mark in 2008, despite various attempts to clamp down on expenditures.

US election authorities say that top-tier presidential candidates like Democrats Barack Obama (news, bio, voting record), Hillary Clinton, and Bill Richardson and Republican Sam Brownback (news, bio, voting record) -- all of whom entered the race just this past week -- likely will need to raise a daunting 100 million dollars by year's end to launch credible campaigns.

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