Depends on what you're comparing...
Both use a gas piston system and tilting bolt that are very similar. As a matter of fact, several articles have been written about the Russians getting the plans for the FN49 from Saive (or others), and several others have claimed that the opposite occurred...
Both rifles fire full power rifle cartridges (.30-06, 7x57mm, 8x57mm and others for the FN49, with later conversions in Argentina to 7.62x51mm NATO) and 7.62x54mmR for the SVT/AVT-40.
Both were made in select fire variants, but not many of either were produced partly because full auto from a 10 rd mag doesn't make a lot of sense...
Both are full size rifles, although the FN49 is somewhat more robust and the SVT-40 more slender and lighter built.
In terms of quality of workmanship and finish, there is no comparison...
Forrest