Your Metro AT is what is generically referred to as a hybrid bicycle, with hybrid referring to it's ability to handle both road and off-road. Essentially, hybrids are ATBs but with 700C wheelsets. I believe Metro AT stands for metropolitan all terrain.

Hybrids did not not have a substantial market impact until the very late 1980s. Your bicycle still has thumbshifters, which were largely phased out in the early 1990s with the advent Rapidfire style trigger shifters. Consequently, I believe your serial number represents late 1989 manufacture and is likely a 1990 model.

Hybrid tyres were a compromise between road and ATB tyres. The width tended to be fatter than road tyres but skinnier than ATB tyres. Most hybrids were designed for 700 x 32C or 700 x 35C tyres, so I doubt there will be an issue. You might even be able to accommodate 700 x 38C but it will be trial and error as all tyres of a certian size do not necessarily measure the same width. The limiting factor is typically the clearance at the chain stays.