TOKYO — Despite objections from antinuclear campaigners, Japan’s government cleared the way on Friday for companies that build nuclear power plants to sell their technology to India — one of the few nations planning big expansions in atomic energy — by signing a cooperation agreement with the South Asian country.

The deal is a lifeline for the Japanese nuclear power industry, which has been foundering since meltdowns at the Fukushima Daiichi power plant in northeastern Japan in 2011. Plans to build a dozen new reactors in Japan were canceled after that, a gut punch for some of the country’s biggest industrial conglomerates, including Toshiba and Hitachi.

With the domestic market moribund, Japanese companies had been pursuing deals abroad, but success was elusive.

The economic case for nuclear energy has weakened as a result of low oil and gas prices, prompting utilities and governments around the world to rethink construction. The Fukushima disaster increased safety concerns. And Japanese vendors have had to fight lower-cost rivals from places like Russia and South Korea for a shrinking number of customers.