Anil Kumble, chief selector Dilip Vengsarkar said, has been rested but the veteran leggie would play the next two matches against Brian Lara's side.
Ganguly also made his way to the list of 30 probables for the World Cup.
Meanwhile, Sachin Tendulkar will be Rahul Dravid's deputy in Sehwag's absence, Vengsarkar added.
In the press conference, Vengsarkar insisted there was not much room for experiment in the side and sang a different tune from coach Greg Chappell, who has been insisting that process was more important that means for Team India.
''We need the best combination and there is little scope for experiments. Winning is very, very important for us,'' Vengsarkar asserted.
The former captain made no bones about the fact that Sehwag was woefully out of form and felt the Delhi bomber needed to spend extra hours in the net to sort things out.
''He is an experienced player and has done well in the past. I think this break willl do him a lot of good and he would come back in the side,'' Vengsarkar said.
Asked if Sehwag's absence would mean Ganguly opening the innings with Tendulkar, Vengsarkar said, ''Well, I can't comment on that for it's up to the coach and captain to decide.''
On Ganguly, Vengsarkar pointed out to the former captain's impressive ODI records, which included more than 10,000 runs, and said, ''If you see his performance in ODIs, it's excellent and he did so well in South Africa.''
On decision to drop Irfan Pathan and leave out VVS Laxman, Vengsarkar said, ''Irfan is clearly out of form and I'm sure he will find his form back and come back to the side.
''For Laxman, fielding remains his problem, as is his running between wickets. He is an excellent batsman but not a great mover in the field,'' he said.
Though Harbhajan ended up as a bench-warmer in the Test series in South Africa, the offie enjoyed the chief selector's backing.
''Harbhajan has done well, especially in the ODIs. Though he did not play in the Test matches in South Africa, he had bowled well in West Indies, especially against the left-handers,'' Vengsarkar argued.
He also asserted that Dinesh Karthik, who shone with the bat in South Africa, was in the side both as a batsman and wicketkeeper.
''He is a player who has got the guts and courage,'' Vengsarkar reasoned.
He, however, ruled out injured Yuvraj Singh's chances of playing in the four-match ODI series against West Indies.
''I don't think he will be fit for the one dayers against the West Indies and we will consider him for the series against Sri Lanka,'' he said.
Asked why the team did not have a single specialist leggie, Vengsarkar shot back, ''Can you name one?'' and then went on to admit that not having enough leg-spinners was a genuine problem for the side.
There was no surprise in the list of probables for the World Cup, which features new faces like Joginder Sharma, Rohit Sharma, S Badrinath, Cheteshwar Pujara, Ishant Sharma and Rajesh Powar.
Squad for 2 ODIs against Windies: Rahul Dravid (capt), Robin Uthappa, Sachin Tendulkar (vice captain), Sourav Ganguly, Suresh Raina, Mahendra Singh Dhoni, Dinesh Karthik, Gautam Gambhir, Zaheer Khan, Ramesh Powar, S Sreesanth, Harbhajan Singh, Joginder Sharma, Ajit Agarkar and Rudra Pratap Singh.
World Cup probables: Rahul Dravid (capt), Robin Uthappa, Sachin Tendulkar, Sourav Ganguly, Virender Sehwag, VVS Laxman, Mohammad Kaif, Suresh Raina, Yuvraj Singh, Mahendra Singh Dhoni, Dinesh Karthik, Parthiv Patel, Anil Kumble, Gautam Gambhir, Zaheer Khan, Ramesh Powar, S Sreesanth, Harbhajan Singh, Joginder Sharma, Ajit Agarkar, Rudra Pratap Singh, VRV Singh, Munaf Patel, Irfan Pathan, Rohit Sharma, S Badrinath, Cheteshwar Pujara, Dinesh Mongia, Ishant Sharma and Rajesh Powar.