George Shultz, Ronald Reagan’s longest-serving secretary of state, didn’t endorse either candidate in this year’s presidential election, even though he’s a lifelong Republican. He declined to disclose who got his vote on Election Day.

But the conservative elder statesman who has worked on U.S. foreign policy for more than 50 years has some friendly advice for President-elect Donald Trump.

Strength and resolve are important, Shultz told me this week; Trump has that part right.

But alliances are essential too. “Without allies, you don’t get anywhere,” he said in an interview at Stanford University, where he’s a fellow at the Hoover Institution.

The GOP foreign policy establishment is willing to help the new president. The issue is whether Trump and his inner circle are willing to accept the hand.

If you want other countries to help achieve U.S. goals, he said, you need to offer them respect, listen to their concerns and cultivate long-term relationships.

“It’s a little like gardening,” he added.

That combination of strength and diplomacy is what enabled Ronald Reagan to win the Cold War, Shultz argued. There’s a lesson there, he seemed to suggest, for Trump — although he said this was advice he would give any president, not a critique of the president-elect.

He said the United States has an interest in a “more constructive” relationship with Russia, something Trump has long called for. “A Russia that’s collapsing, with thousands of nuclear weapons, is the last thing we need,” he said.

But he also said the three Baltic countries, which feel threatened by Russia, “need reassurance” that the North Atlantic Treaty Organization will defend them. (During the campaign, Trump said he might not defend NATO countries that aren’t spending enough on defense. But President Obama said this week that Trump intends to maintain the U.S. commitment to NATO.)

Shultz suggested that Trump seek broad-scale talks with China, too. “The new president should say to the president of China: ‘Why don’t you and I … get together and make a list of all the things where collaborative action on our part would be beneficial?’” he said. “And then list what are our points of tension and what can we do about them … and let’s work our way through that agenda.”

There’s still work to do to prevent proliferation of nuclear weapons, he added. At one point in the campaign, he noted, Trump said Japan and South Korea might need nuclear forces.

Bad idea, Shultz said, noting that Trump later abandoned the suggestion. “The more you proliferate, the more chances you get that someone will set one off,” he said.

One more issue Shultz hopes the president-elect will think about: climate change.

“People who say the climate isn’t changing are in the process of getting mugged by reality,” he said. “Zika is the tip of the iceberg. With climate change, tropical diseases are coming north, carried by mosquitoes…. and we’re not ready for it.”

Trump was never Shultz’s first choice for the GOP nomination. “God help us,” he told reporters in an unguarded moment in August.

But he’s keeping an open mind now. “Fingers crossed,” he said.

Shultz confers often with another former secretary of State, Henry Kissinger; they’re both willing to help the new administration find its footing in foreign policy.

Is this a cynical, Washington-style conversion by mandarins who want to curry favor with the new boss?

“I’m not looking for a job,” Shultz joked. He’s 95.

In truth, it sounds more like old-fashioned patriotism — an offer from an elder statesman to help a new team avoid rookie mistakes.

Bottom line: The GOP foreign policy establishment is willing to help the new president. The issue is whether Trump and his inner circle are willing to accept the outstretched hand. That’s still an open question.

Last week, Eliot Cohen, a former official in the George W. Bush administration who denounced Trump as unfit for the presidency, encouraged national security experts to help the new administration.

“If anything, having professionals serve who remember that their oath is to support and defend the Constitution — and not to truckle to an individual or his clique — will be more important than ever,” Cohen wrote in the National Interest.

Then Cohen talked with Trump’s transition staff. It didn’t go well.

“Changed my recommendation: stay away,” Cohen wrote Tuesday on Twitter. “They’re angry, arrogant, screaming ‘You lost!’ Will be ugly.”

Doyle McManus is a columnist for the Los Angels Times. Readers may email him at doyle.mcmanus@latimes.com.