It is getting close to crunch time in the developing security and strategic relationship between India and the United States, and it looks as though one side is getting a little nervous. Think about it like a person, long considered to be a confirmed spinster, who surprises all by deciding to get hitched, then has a fit of nerves ahead of the nuptials.

For the past three decades, the world's biggest democracies have danced around each other, inching forward a step at a time. Although not exactly on "opposite sides of the Cold War" as many like to portray, there certainly was no love lost between their leadership. In the 1950s, John Foster Dulles considered Pandit Jawaharlal Nehru's nonalignment policy "immoral". Nehru in turn thought the US Secretary of State was "dull, duller... Dulles!" In the 60s, President Richard Nixon, his insecurities triggered by Indira Gandhi's moody silences and air of lofty superiority, referred to the Indian leader as "an old witch" in conversations with Dr Henry Kissinger.

Nixon's famous "tilt" to Pakistan during that country's 1971 war with India over Bangladesh did not help. Perhaps Nixon knew that Nehru referred to him as a "nitwit" in the days he was vice-president to Dwight Eisenhower.

But the Soviet Union, with which India had a treaty relationship, collapsed in 1991 and India began to reconsider its options. Things stirred during the George H.W. Bush administration. During the first Gulf War, New Delhi provided American warplanes refuelling facilities while on their way to Operation Desert Storm. It was a small step that led to bigger ones, including the Next Steps in Strategic Partnership during the Atal Behari Vajpayee years that culminated in the civil nuclear deal signed by President George W. Bush and Prime Minister Manmohan Singh in 2006.

That agreement is now considered the watershed event in bilateral ties. New Delhi felt a warm glow as the US declared its intention to help make India a "major power in the 21st century". Indians "love you", Dr Singh gushed to Bush Jr even as the US leader endured a period of deep unpopularity in his own country.

Subsequently, as defence ties grew apace, it promised to help bring the most advanced technology to India's indigenous aircraft carrier building programme. At the US Pacific Command, the talk turned from references to the Asia-Pacific, to Indo-Asia-Pacific, crunched latterly to just Indo-Pacific. The US gave Indians more H1B work visas than to any other nation.

For its part, India began steadily expanding its strategic ties with the US. Today, the US conducts more military exercises with India than with any other power. A joint strategic vision unveiled during President Barack Obama's trip to India in January last year surprised all by its boldness. "We affirm the importance of safeguarding maritime security and ensuring freedom of navigation and overflight throughout the region, especially (emphasis added) in the South China Sea," read the most remarked upon part of the statement.

But all that had to lead somewhere. And it has. As it resists being boxed into its neighbourhood by an increasingly assertive China, India has been sending naval ships into the South China Sea for regular patrols. Port calls, especially to Vietnam, which has testy ties with China, have increased. Last year, after a five-year gap, India once again invited Japan to Exercise Malabar, the annual war games it conducts in the Bay of Bengal with the US.

Years ago, when the Australians also had been invited to discuss security cooperation, China saw red at this "quadrilateral" as it was called and warned that the efforts should not be targeted "at a third party". India, mindful of Beijing's sensitivities, went slow thereafter. Now the US is pitching for a revival of the quad, saying it would be a logical extension of the trilateral dialogue hosted by New Delhi last year that also involved Tokyo and Canberra. It could well happen.

Less than a decade ago, when Indian navy chief Sureesh Mehta announced Exercise Malabar would be held in the Bay of Bengal, Mr A.K. Antony, India's defence minister at the time, hit the roof. Mr Antony, aware of China's sensitivities, demanded to know why the navy was planning this exercise in the Bay when Malabar, the region after which it is named, was on the side of the peninsula that faced the Arabian Sea.

But under US pressure, this year's Exercise Malabar, which will again involve the US and Japan, is to be held even farther afield - in waters just north of the Philippines and close to the South China Sea. That's a measure of how swiftly the security landscape is changing.

It is a significant move and up to a point, India seems ready to go along. When Mr Manohar Parrikar, the current Indian defence minister, visited the Pacific Command last year, the discussions even involved joint patrols in the Indian Ocean. But that's a large expanse of water. The US is now demanding more; pressing India for joint patrolling in the South China Sea and even independent freedom of navigation operations (Fonop). That's where the nerves are starting to show as New Delhi weighs the implications of a move that it is not quite ready for. It is also angered that the Americans are pushing India publicly on sensitive subjects best discussed behind closed doors.

Last week, Mr Parrikar firmly said that "the question of joint patrol does not arise".

For India, the issue is this: Were this about some Chinese incursion in a section of their undemarcated border that India considers within its territory, it would be a different matter. But the South China Sea - even if those egging India to take a firmer stand point out that 55 per cent of Indian trade transits this region - is not exactly a core interest. Besides a good part of that trade is headed to China. Surely, Beijing is not going to down ships carrying cargo it has paid for, or carrying goods it is selling to India!

It is one thing to state general principles, quite another to risk major trouble over it. China may wince and complain if the USS Lassen or USS Caffee transits the territorial waters of its artificial islands without its express permission but a Fonop by the INS Rajput or INS Mysore would be another matter. India gains little by poking China in the eye, especially when Beijing sits on higher ground in the Himalayan border and has any number of levers to pull in India's sensitive north-eastern states, not to speak of its "all-weather" friendship with Pakistan that Beijing can count upon in any number of ways.

But it is not just the maritime part of the equation where New Delhi and Washington are having to work on their issues. Indians are proving difficult even in areas where they could yield a little. Trade, for one, is throwing up difficulties. India's Commerce Minister Nirmala Sitharaman is despised in Washington for her intransigent positions. For her part, she frets that US negotiators tend to be too unsympathetic to Indian concerns and rude - "even wagged a finger in my face!" - she complained to friends some time ago.

More recently, the spat between Monsanto, the US chemical company that revolutionised cotton farming in India by introducing genetically modified strains to farmers in Prime Minister Narendra Modi's Gujarat state, and a government that insists that the company lower seed prices by more than half - is heating up.

In their joint strategic vision, the US had welcomed India's interest in joining the Asia-Pacific Economic Cooperation forum but within 10 months, ardour on that front had visibly cooled. As he headed to Manila last November for Apec, Mr Matt Matthews, the senior US official for Apec, said firmly that discussion on India's entry into the forum was "not on the agenda".

It was always going to be difficult for a nation so large as India, with its diverse interests and massive geography, to move away from its centrist path in policy - foreign or domestic. Long term, there is little to be gained by an adversarial relationship with China. Indeed, their mutual dependence will only grow as India's economy expands swiftly from its lower base while the mainland slows. Beijing will need access to India's markets and investment opportunities for its own future expansion. India will need Chinese capital.

Meanwhile, US ardour to keep India entirely in its corner shows no signs of cooling. Admiral Harry Harris, the head of Pacific Command, last week called the US-India relationship "the defining partnership of the 21st century".

"We are ready for you. We need you," he said at a security dialogue in New Delhi, repeatedly clearing a throat evidently affected by the city's pollution. But New Delhi is taking its time. Approaching its 70th year as a free nation, India, even if she is not fainting at the altar, is clearly a little spooked. Maybe it also wants to see how the US election plays out before making firmer commitments. US presidents try to deal with China in their first term, then turn to India in the second, although a Hillary Clinton presidency would be an altogether different matter. At any rate, it does not look like the country is in any mood to be rushed. Mr Modi's India is not Mr Shinzo Abe's Japan, never mind the close friendship they enjoy.

In strategic affairs as in life it is one thing to show a bit of leg or permit an occasional cuddle, quite another to take things all the way.