The money will help fund the reelection bid in 2010 for the Patrick-Murray ticket, a campaign spokesman for Murray said.
It is also fueling speculation that Murray is preparing for an inevitable run for the state's top office at some point in the future.
"We fully expect to be running for reelection in 2010 and we want to have a strong campaign ready to go," said Murray's campaign spokesman, Michael Cohen.
"Tim Murray understands the importance of having a strong campaign."
By contrast, Coakley raised $174,416 through mid-August, just slightly more than Cahill with $164,530. State Auditor Joseph DeNucci and Secretary of State William Galvin raised less than $100,000, although Galvin reported a balance of more than $510,000 in his campaign account.
Murray's fund-raising effort ramped up through the first half of the year, peaking in June, when he raised more than $132,000 in a single month.
The donations ranged from as little as $10 to $500, the maximum allowed by state law.
The $545,000 Murray raised through July is also more than twice the $264,000 he raised during the same time period in 2007. Contributors include unions, state troopers, lawyers, political action committees, teachers, developers, and CEOs.
A significant amount of the money has already gone into savings accounts, to be tapped when needed. Cohen said Murray has about $450,000 in the banks. He has also spent money on staff payroll, rent, catering, and printing expenses.
It makes sense for Murray to stockpile campaign cash, not only for any reelection campaign with Patrick, but just in case Patrick's political fortunes change if Barack Obama is elected president, observers said.
"For Tim Murray, there's nothing like putting away the money for that rainy day and that rainy day could be Deval Patrick being appointed to an executive position if Barack Obama is elected," said Tobe Berkovitz, associate dean of Boston University's College of Communication.
Either way, Berkovitz said, "it's just common sense that any politician should be raising money throughout their term in office."
Murray could use the money to help discourage any potential challengers to the administration, either Democrat or Republican, although none have yet emerged.
"We're focused on winning seats for '08 and helping win Massachusetts for John McCain," said state Republican Party spokesman Barney Keller.
