The former Wales and Leeds Rhinos rugby league captain has scored more than 50 points, including four tries, in two and a half matches for Cardiff in the last three weeks and will go into the game partnering Rob Howley at half-back.
Wales coach Graham Henry said: "Iestyn Harris has ample experience of playing at the top level. I'm certain he will fit in more than adequately in this new environment. With Scott Quinnell at No 8, Rob Howley at No 9 and Stephen Jones at No 12, we have people of experience and authority around him who can make decisions themselves and help take some of the pressure off his shoulders
"We've had a number of close and tough encounters with the Pumas in recent years and they have always tested us. They will believe they can beat us for the first time at the weekend and we will have to be at our very best to come through. There is a lot to prove after the defeat against Ireland, both to ourselves as a team and to the Welsh rugby public. This is a challenge the players are very much looking forward to and the countdown to the 2003 Rugby World Cup starts here."
There could also be a first full cap for Harris' former Wales and Great Britain rugby league team mate Anthony Sullivan. He is standing by to replace Shane Williams should the Neath wing's knee injury not respond to treatment.
Back after injury are two of last summer's Welsh Lions, Darren Morris and Scott Quinnell, along with Bridgend centre Gareth Thomas, and they will pack down in a side showing eight changes from the team beaten 36-6 by Ireland in Cardiff in last month's Lloyds TSB Six Nations match.
Out go Allan Bateman, Leigh Davies, Iestyn Thomas, Chris Wyatt, Brett Sinkinson and Geraint Lewis, while Stephen Jones switches position. Dafydd James was not considered because of his shoulder injury. Bateman, Thomas, Wyatt and Sinkinson all feature among the replacements.
Wales team manager Alan Phillips said: "The new players will bring a new impetus to the team. Many have things to prove both in terms of their standing in the pecking order and their positional preference."
The game will be the sixth full capped game between Wales and the Pumas. Wales have won all five to date, including the opening game of the 1999 Rugby World Cup, 23-18, when the two teams last met.
WALES: Kevin Morgan (Swansea); Rhys Williams (Cardiff), Gareth Thomas (Bridgend), Stephen Jones (Llanelli), Shane Williams (Neath) or Anthony Sullivan (Cardiff); Iestyn Harris (Cardiff), Rob Howley (Cardiff); Darren Morris (Swansea), Robin McBryde (Llanelli), David Young (Cardiff), Craig Quinnell (Cardiff), Andy Moore (Swansea), Colin Charvis (Swansea), Gavin Thomas (Bath), Scott Quinnell (Llanelli).
Replacements: Barry Williams (Neath), Iestyn Thomas (Ebbw Vale), Chris Wyatt (Llanelli), Brett Sinkinson (Neath), Dwayne Peel (Llanelli), Jamie Robinson (Cardiff), Allan Bateman (Neath)