"It could lead to humiliation at the hands of our neighbors," AK Sachdev, a retired air force officer, wrote last year in the Indian Defense Review journal.
A coordinated attack by China and arch-rival Pakistan could stretch the Indian military, he added. It's a scenario defense strategists in New Delhi have been asked to plan for, Indian air force sources say, although experts say such an event is highly unlikely to happen.
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India's ties with China are still hamstrung by a dispute over their Himalayan border that led to war in 1962. New Delhi is also wary of China's expanding naval presence in the Indian Ocean and its close relations with Pakistan.
India's air force has 34 operational squadrons, down from 39 earlier this decade and below the government approved strength of 42, a parliamentary committee said in December.
More than half of India's MiGs have crashed in recent decades, the then defense minister said in 2012.
At the same time, China is flying locally built fourth-generation J-10 fighters and is testing two fifth-generation stealth fighter jets.
Pakistan is upgrading its Lockheed Martin F-16 fighters as well as using JF-17 warplanes developed with China. It is also in talks to buy J-10s, according to Pakistani and Chinese industry sources.
India would still win a war against Pakistan because of the sheer size of its air force, but the slow modernization means victory would come with heavy casualties, said Richard Aboulafia, Washington D.C.-based vice president of analysis at the Teal Group, an aerospace and defense think tank.
To keep up, India is buying more Su-30s and upgrading other existing fighters.
"We do need to increase our defense preparedness," Prime Minister Narendra Modi told the opening ceremony of the Aero India airshow in the city of Bengaluru on Wednesday.
Criticism of the Tejas was unfounded, said K. Tamilmani, a senior official at the Defence Research and Development Organisation (DRDO), a defense ministry agency which designed and developed the plane.
"The Tejas has a safety record that is unbeaten," Tamilmani told Reuters by telephone, adding it would provide a platform to develop more advanced fighters in the years ahead.
Impasse over Rafale jets
The Rafale fighters are expected to replace some of India's MiGs and Mirage jets.
But India is insisting Dassault take full responsibility for production of the aircraft at a state-run facility in Bengaluru, Indian defense ministry officials have said.
France has said it will help Hindustan Aeronautics Ltd stick to delivery schedules, but that it cannot give guarantees for production of the aircraft made at a facility over which it has no administrative or expert control.
India would decide on the fate of the deal only after March, when a defense ministry committee delivers a report on the issue, Defense Minister Manohar Parrikar said at the airshow.
Cancellation would be "disastrous", said Deba Mohanty, chairman at Indicia Research & Advisory, a New Delhi-based defense consulting firm.
"It's a really tricky situation in which the supplier is unhappy, the bureaucrats are unhappy and the end user is disappointed," said Mohanty.
India has successfully introduced Boeing's C-17 cargo plane and P-8 Poseidon anti-submarine aircraft and Lockheed Martin's C-130J transport, all bought directly, over the last few years.
That shows off-the shelf solutions work best, experts said.
However, under the Modi administration's "Make in India" program, there is an emphasis on building a domestic defense industrial base to cut dependence on foreign supplies that have made India the world's biggest arms importer.
The DRDO for example is working on the Tejas Mark II, a slightly larger plane than the original, which will feature more powerful engines, better radars and upgraded avionics.
Local trainer jets, light transport aircraft and helicopter programs are also under way.
"People who fly planes want the best value for money, which means off-the-shelf," said Aboulafia. "People who want jobs and technology development schemes have different priorities. That's why the two groups don't like each other much."