NEW DELHI—Political realities are putting the brakes on Prime Minister Narendra Modi’s plans for economic revitalization 15 months after Indian voters gave him an overwhelming mandate for change.

After nearly a month of partisan bickering, lawmakers ended a parliamentary session Thursday without passing a centerpiece of the prime minister’s agenda—a constitutional amendment to replace a thicket of varying state taxes with a more business-friendly nationwide levy.

The Indian leader, worried about political opposition and a backlash from rural voters, also effectively abandoned efforts to win approval for another measure to spur development—legislation that would have made it easier for the state to acquire land for infrastructure and industry.

Mr. Modi swept to power with his impassioned pledges to reset India’s economy, a promise he has consistently repeated on visits to world capitals during his tenure. But blocked by the opposition and reluctant to take risky political steps, his liberalization project is languishing.

On politically sensitive issues such as the land bill, Mr. Modi’s Bharatiya Janata Party is determined not to anger the country’s rural masses, who make up 70% of India’s population, ahead of pivotal state-level elections.