Back in the heady days of 1970s feminism there was an argument that once women achieved political power, there would be no more war. Margaret Thatcher and her Falklands war exploded that myth, and along with it any residual notion that women might do foreign policy differently from men. Indeed, it became a credibility requirement for any women with a senior foreign or defence brief to give a wide berth to anything with a whiff of being a woman's issue. Women had to work extra hard to look tough on the world stage. Meanwhile, women's issues were parked in the softer brief of international development.

It is these unspoken rules that Hillary Clinton has been dismantling since becoming US secretary of state two years ago. She is the most powerful politician to advance an explicitly feminist agenda. Even in that most delicate and crucial relationship with China – on which the world's attention will be fixed this week for the Chinese president's visit to the US – Clinton has gone out of her way to press feminist issues. In China's case, she has highlighted the country's growing gender imbalance caused by the high abortion rate of female foetuses.

Inevitably, some see it as a recasting of US imperialism, others as a force for the progressive good. I'll come on to what it stacks up to, but the first point is to marvel at how she has got away with it. On countless occasions since arriving at the state department, Clinton has asserted that the rights of women and girls are now core to US foreign policy. It's hard to imagine any British foreign secretary ever saying such a thing.

Many of her statements can be routed back to the idealistic internationalism of 70s feminism. Astonishingly, she has managed to bring the feminism for which she was loathed in the early 90s (as the first lady who didn't stay home and bake cookies) into the heart of the state department and foreign policy, and is still clocking high opinion poll ratings.

From the start Clinton left no one in any doubt where she stood: women's rights are "the signature issue" of this administration's foreign policy, she said. She mentioned women 450 times in speeches in the first five months in office. "Transformation of the role of women is the last great impediment to universal progress," she declared, and began to develop what is her standard line: women's issues are integral to the achievement of every goal of US foreign policy.

Or put more simply: the empowerment, participation and protection of women and girls is vital to the long-term security of the US. Last month this rhetoric was translated into policy in the long awaited Quadrennial Diplomacy and Development Review, which aimed to redefine US foreign policy around civilian power. "We are integrating women and girls into everything we do… in all our diplomacy with other governments… in our work on conflict and crisis," said the state department's briefing.

For a security agenda traditionally dominated by weaponry and military expertise, this is radical stuff. It draws on a powerful consensus built up behind the overwhelming evidence that women are vital to a range of key global concerns. Links have been drawn between gross gender inequality and political extremism. Women are crucial on issues such as food security (women produce most of the food that feeds the world), health, education and democracy. The World Bank picked up this agenda long ago, and a raft of unexpected allies have emerged, such as the economist Lawrence Summers, who said that the most effective investment in development is the education of girls. Clinton has been riding a wave of optimism that women hold the key to global development and peace.

She makes this abstract thinking concrete on her foreign visits. Her press entourage finds itself dragged around meetings with micro-credit groups, activists and politicians – all women. It's strategic, she admitted in an interview – "It's a constant effort to elevate people who, in their societies, may not even be known by their own leaders. My coming gives them a platform, which then gives us the chance to try and change the priorities of governments." When she visited South Africa, she spent twice as much time with a women's housing project as she did with the president.

She has carefully chosen key issues and pushed hard. Perhaps her greatest success so far has been to highlight sexual violence as a weapon of war. Anne Marie Goetz of UN Women argues that sexual violence is an "even more destructive weapon than landmines or cluster bombs on communities because its effects are so long term", but repeatedly the issue was marginalised or ignored in conflict resolution or peacekeeping.

In 2009 Clinton visited the Democratic Republic of the Congo and talked to rape victims, and she has been instrumental in the passage of a series of UN security council resolutions that have put real teeth into tackling the issue: the appointment of a special representative last April – Margaret Wallström – the naming of perpetrators, and a dedicated team of experts to pursue them.

Clinton was also key to setting up UN Women, which started work last week. In particular, she is credited with persuading the former Chilean president Michele Bachelet to take the top job.

Take another issue for which women's groups had struggled to get recognition. One of the biggest killers of women and children in the developing world is cooking stoves. Inhalation of smoke from open fires kills 1.9 million a year. Plus, gathering firewood makes women and girls vulnerable to sexual violence, quite apart from the environmental consequences of chopping down trees. Yet the issue has had a fraction of the attention of Aids/HIV or malaria. Last September, Clinton launched a global alliance for clean cookstoves with a US pledge of $50m and a target of 100m stoves by 2020. One observer said: "It was classic Clinton, very practical; it's modest but makes a massive difference – but it took a woman to get it."

Observers on both sides of the Atlantic acknowledge "she's a game-changer". They say the prominence she gives key issues enables them to be taken seriously. But for all the enthusiasm, it's clear there are major constraints on this agenda. It gets nowhere in the Middle East, while Afghanistan presents a big challenge – Clinton has insisted peace cannot come at the cost of women's rights. But the signs aren't good that she can hold this line. Meanwhile, there are critics who worry that her advocacy could backfire and antagonise conservative societies, and even prove inimical to US interests.

It could generate resentment and suspicion, says Stephen Walt, a professor of international relations at Harvard. He points out the US can't even sort out its own problems of sexual inequality, so it is "overly optimistic" to think it can have much impact in Yemen, Congo or India.

Clinton is careful to couch her feminism in talk of US interests and splice it into a hawkish toughness to reassure her domestic audience. She has picked her issues carefully, and made some big compromises to keep people on side. Her feminism has obviously been helpful for the Obama administration, which is anxious to redesign US foreign policy in the midst of two disastrous foreign wars. It could still reap dividends for women, but the question is: will it be quietly sidelined when no longer useful?