Can I put heavy table with marble top and steel legs as well as steel chairs out on a wooden deck?

T.J. is right. There are just too many factors here that we are not knowledgeable of. It will help if you locate the support beams underneath so that as much weight as possible in on them. And you could distribute the weight more evenly if you put down a piece of plywood and then set the table on top of that.

That would depend on how heavy the table is and how well constructed the deck is.

A properly constructed deck should be able to hold any normal load without sagging, including an average size marble table. If I built your deck it would have no problem holding the weight, but I didn't build your deck so I really can't say for sure.

Unless the deck is a piece of crap it will easily support such a table. If your worried sister the floor joists below the table.