One short-term job offer and an interview for a long-term contract?

On Friday I got two call backs from two different temp agencies. The first one has a 3 week assignment with no interview for $11.50, medical file clerk. It starts June 1 and I accepted it already. Later that same day I checked my phone and set up and interview for an Administrative Assistant job for $12-$15 per hour and it's a year long contract.

So I interview this Tuesday and have to sign papers for the other job, drug test, and whatnot the same day. I'd like to hold out for the better opportunity, but I may not get it. I've been out of work for a long time and could use the money. I'll probably ask when the job starts in the interview because if it starts in July I could do both. I may end up burning a bridge if I can't finish the assignment if I start that, but it's doggy dog out there and few opportunities arise in this recession.

Please let me know what you would do in this situation. I'm asking this again because people keep sending me links to scams. Please do not advertise!!! I'm looking for opinions or suggestions only.
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You don't have enough information to base a sound decision on. You need to find out when the long term job starts. I would put off signing papers for the first job, for one day if possible, till you can find out more about the long term job.
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I would actually try telling the job offer that pays less the truth and see if they are willing to work with you so you can do both jobs. I would even make sure the day I start with the other company is my last day or that you can have it off. Try not to bun any bridges but ask for help while you are in a position to get it. Most employers are willing to help if they know the truth and really want you.
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How soon will they contact you for the long-term position? You still have a week before June. If that accepts you, take it and go for it because its good money. Try calling in the week to thank the person for an interview or something if you don't get any news after a couple days.