Walker, 35, has impressed since joining the Us from West Ham United, making a crucial penalty save in the 1-0 win at home to Leyton Orient on Sunday.
Lambert told the East Anglian Daily Times: "Jimmy Walker is a brilliant keeper. He has been a massive help since he's been here.
"He's a top, top goalkeeper. In fact, I rate him as highly as Scotland's Andy Goram. He's that good.
"I'd like to bring Jimmy in on a permanent basis. His last game is this Saturday, but I'll be doing my best to keep him at the club."