Front deck sagging....what is the 'proper' method to fix it?

Hi all,
My front deck is sagging noticeably in the middle. The deck itself is approx. 4' x 16', and is used only as an entrance/exit (no BBQ, furniture, etc.). The deck surface is about 1.5' (avg) above ground level.
There are support 4x4's running vertically at each end of the deck, and one support in the middle. The supports extend just over 8' to a roof overhang above. It is clearly noticeable that the middle 'support' post is not even touching the underside of the overhang anymore....based on this, it looks like the middle portion of the deck has sagged about 1".
Also, at ground level, it looks like the post simply terminates at the ground, with no concrete or blocking of any kind. I presume the best solution is to jack up the deck in the middle, place a pre-formed concrete block/slab (or even PT wood) beneath the 4x4, and simply remove the jack.
However, any suggestions on what type of jack to use, or any alternative method would be greatly appreciated. I should mention that because it is a front deck, the 4x4 support posts are shrouded with 1x4 running horizontally (to hide the underside of the deck). This could make access difficult; I expect that I would have to remove one or more of these planks first.
Cheers, Dave
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I have lifted entire small barns / sheds using nothing but a mechanics floor jack. Of course I have a 4 tonner, not one of those dinky things they sell for $19.95 for compact cars. I mean a REAL jack that can lift a SUV or pickup truck. One thing to remember. The jack tips toward you, so place it on a solid, and level foundation, so the wheels can move with the jack. If it starts pulling the deck toward you, stop, pile cement blocks and wood scraps, and reset the jack.
After you get the deck leveled on piles of blocks and wood scraps, replace the posts with treated 4x4's or larger. It may pay to pour a footing under it too.
On 1 Jul 2004 17:59:04 -0700, dave snipped-for-privacy@hotmail.com (Borrall Wonnell) wrote:

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dave snipped-for-privacy@hotmail.com (Borrall Wonnell) wrote in message

The deck supports should have footings that extend below the frost line, not be resting on the ground or on concrete slabs. You need to dig holes, put forms in, and fill them with concrete.
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