Panagariya also favoured continuation of cess, dismissing criticism that it would dilute the original idea of a single unified rate.
Explaining the rationale behind the proposed four rates under GST, he said: "...Big gains from GST will be because of having a single rate across any given product geographically."
The GST Council is discussing a proposal to have four-slab tax structure for GST with 6, 12, 18 and 26 per cent along with an additional cess for luxury and demerit goods.
Earlier in the day, former finance minister P Chidambaram said the proposed multiple rate GST structure will be "disastrous" and nothing more than same old VAT rates in a "new shape".
"We sincerely hope that we do not misinterpret the design of standard, standard minus and plus rates of GST. We can have 20 rates. It will be disastrous and that cannot be GST, it will be fooling the country," Chidambaram told an interactive session with IIM Calcutta students on economic reforms.
He added: "A lot of people think that they have identified single tax rate across commodities. But the bigger part is single tax rate on every product across entire country. There is no tax theorem that two rates are better than four."
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Observing that GST is a process and the country would head towards one tax band, Panagariya said it cannot be done in one go as it would fuel inflation by pushing prices of some of the adversely impacted commodities.
"This way (having four rates) doing it has an advantage that your tax revenue loss prospects are less. It is more predictable. Even a one percentage point mistake will lead to much bigger impact (on revenue). It (four slabs) will help you to ascertain revenue in the beginning," he said.
On continuation of cess he said, "There is devolution issue. 42 per cent (of tax collections) goes to states. Cess is 100 per cent with the centre."
About meeting GST roll out deadline (April next year) he said: "Government is working towards it and there is no reason why I should believe that it will not happen.
"It's a little bit of race against time but certainly well within the realm if possibility.
