Wood, Metal, Plastic?
Typically, for wood, I take some stout round toothpicks (About 3, depending on size of hole) Add some wood glue, a very little bit (gorilla might work best as it remains pliable). Ram them in the hole, let it sit for a few hrs (let glue start to set up), then run the screw in (as assembled) ALMOST all the way while applying significant force inward to keep toothpicks from coming outward, I let it set up better (~ 6-10 hrs) then tighten up the screw. You might want to have a piece of Wax Paper between leg and table if there is any glue dripping (And if you plan on moving again and not using a saw to remove the leg...)
You can probably find a woodworker handyman by inquiring at Woodcrafters in Portland (or they will have a kit to repair threads with an insert)
Woodcrafters Home Page
212 NE 6th Ave
Portland, OR 97232
(503) 231-0226
or similar help here
Crosscut Hardwoods Eugene, Portland, Beaverton, Hillsboro Seattle Lumber Plywood Decking 503-224-9663
(Unfortunately we lost out furniture wood supply Lumberyard in Vancouver...Bergerons, now Winco / Andreson lot) (Just across street from Old Friends see below)
I have had these guys do some stripping for me (They do refinishing too, and I think light repair)
Old Friends Furniture Stripping
7215 NE 18th St # B
Vancouver, WA 98661
(360) 604-8565
For metal, (and plastic) go to Parkrose Hardware and get a Helicoil / thread-sert kit (take your screw with you). Since they are close to you, (164th Ave and East 1st st) they might have a handyman listing. Some plastic insert repairs may require epoxy (JB weld works pretty well) coat screw with WD-40 or light dose of Vaseline so it can be removed later.
If you need a new dining room table

,(or just to drool over their hand-rubbed finish...) swing by The Joinery, on your way to the Rhodie Gardens (just about time for that awesome experience)
Portland Parks & Recreation :: Crystal Springs Rhododendron Garden
the folks at The Joinery would be happy to tell you how fix your wood table.
4804 SE Woodstock
Portland, OR 97206
(503) 788-8547
If none of this works... PM me.