Reaping the benefits of low global prices for oil, India's main import, Modi's government sees itself in a sweet spot with spare cash to modernize ageing roads and railways without busting fiscal deficit and inflation targets.
"Let us stop unnecessary expenditure so that money can reach the poor," Modi told parliament on Friday after a finance ministry report committed to bringing the fiscal deficit down to 3 percent of gross domestic product - from more than 4 percent at present - in the medium-term.
Budget 2015: Complete Coverage
"We believe in optimum utilisation of our infrastructure," he said.
An overhaul of economic data has propelled India to the top of the league of fast-growing major economies, and the current account deficit is projected to fall below 1 percent next year, which would help stabilize the rupee and build up reserves.
But expectations for a further shift in expenditure from subsidies to infrastructure are sky high among investors who made India the best performing stock market in Asia after China last year on hopes Modi's government brings sweeping reforms to labour, tax and land laws.
Spanish bank BBVA described the budget as "the best opportunity for India to kick-start major structural reforms".
The rally has continued this year on expectations that legislative reform will push ahead stalled private investment and consumer demand, and reverse a decline in corporate earnings to make Asia's third-largest economy a global growth driver.
The stakes are high after a part-year budget that disappointed investors just after the government took over last year with a large majority in the lower house of parliament.
Analysts warn that Indian stocks are overvalued and that equity markets could see a sell off of 6-8 percent if the pro-growth measures in the budget, to be unveiled by Finance Minister Arun Jaitley at 11.00 a.m. (0530 GMT), fall short of expectations.
Modi has capitalized on low oil prices to shake off some of the fuel subsidies that have hobbled India's national accounts for years. But he has been unable to pass reform in the upper house of parliament, where his party has no majority.
Executive orders he has used to push key polices such as land reform will expire unless he can win opposition support.
On December 30, less than a week before he was named Modi's top economic advisor, former Columbia professor Arvind Panagariya warned that this budget was make-or-break for Modinomics.
"Without a clear road map of reforms in it, the dream of 'good days' will run the risk of becoming history," Panagariya wrote in the Business Standard newspaper.
(Additional reporting by Rajesh Kumar Singh in New Delhi and Dipika Lalwani in Mumbai)
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