Various Australian prime ministers have flirted with the idea of asking to join, but have never proposed it while in office. Joining South-East Asia's premier association of nations would underline Australia's importance in the fast-growing region.

It is the first time an Indonesian president has endorsed the concept: "I think it's a good idea," president Jokowi said as he prepared to travel to Sydney for the weekend summit of the 10 ASEAN leaders with their Australian counterpart.

Indonesia is the leader of the 10-nation grouping, making his intervention potentially highly significant.

In an exclusive interview after Fairfax Media spent a day in Banten province with him on the central island of Java, the president universally known as "Jokowi" signalled he wanted Australia to play a larger role in the region in defence, trade and security matters.

Asked about Austalia joining ASEAN, he said he endorsed it “because our region will be better, [for] stability, economic stability, and also political stability. Sure, it will be better”.

Told of his remarks, Australian Prime Minister Malcolm Turbull responded: "I will look forward to discussing that with President Jokowi if he raises it with me".

"We would wait to be invited," he told Fairfax Media. "We treat ASEAN and the centrality of ASEAN in the region with the greatest respect."

Mr Turnbull has invited president Jokowi to dinner at his home tomorrow night ahead of the two-day summit, the first time Australia has hosted an ASEAN leaders' meeting.

The president said the private dinner "means we are very close; this means there is mutual respect".

The Indonesian leader said he was not sure whether Australian membership of ASEAN would be supported by the other members of the bloc, the chief political and economic grouping of South East Asia for the past 51 years.

The president also threw his weight behind finalising the delayed Indonesia-Australia free trade deal, possibly as soon as this weekend. "I will push my ministers", he said.

He also left open the possibility of reviving a Keating-era security pact while stressing the close relationship between the two nations.

Former prime minister Paul Keating, who has long argued for full Australian membership of ASEAN, said Australia could bring skills and expertise in foreign policy to the grouping.

“I have always believed that our nearest, largest neighbour was the one most likely to see the sense and the benefit of Australia joining ASEAN. I am very gratified to hear that President Jokowi has said what he has said.”

“In doing so, he has underlined and confirmed my faith in Indonesia as one of our greatest friends, and so singularly important to us.”

ASEAN is headquartered in Indonesia, its biggest member. ASEAN's other nine members are Malaysia, the Philippines, Singapore, Thailand, Cambodia, Brunei, Vietnam, Laos and Myanmar.

In 2002, the then Malaysian Prime Minister Mahathir Mohamad thwarted John Howard's attempts to engage more deeply with ASEAN, while the then Indonesian president Megawati Sukarnoputri expressed reservations too.

Earlier this week, former Indonesian foreign minister Marty Natalegawa – a friend of Australia's – said the membership question was a “distraction,” while former ASEAN secretary-general Rodolfo Severino said in 2017 that Australia couldn't join because it's just "not Southeast Asian".

ANU Indonesia expert Dr Greg Fealy said: "The question is whether the other ASEAN countries would agree. ASEAN works on consensus so if you don't get universal agreement it won't happen."

On the eve of the historic ASEAN-Australia summit in Sydney President Jokowi said that only “technical details” of the delayed free trade agreement between Australia and Indonesia remained to be settled.

"The bilateral relationship with Australia is very strong, very strong," he said.

He had originally called for it to be completed by the end of last year.

On the defence pact struck in 1995 by Mr Keating and former president Suharto – which marked an historic high point in relations between the two nations – President Jokowi chose his words carefully but did not rule reviving such a close arrangement.

“I think it depends on the government. If we want to make our relations stronger, it’s always from the government, always from the leaders. I’m sure if the communication is like now, we won’t have a problem in our relations.”

The president also praised the close co-operation on counter-terrorism between the two nations.

The President and Prime Minister had spoken regularly on the phone, Mr Jokowi said, to resolve issues such as the threat posed by Islamic extremists who last year seized the Philippines’ city of Marawi.

“We have good cooperation on Marawi, not only with Australia but also with Malaysia, with the Philippines, with Brunei. You know that no country is invulnerable from terrorism or extremism. However, in Indonesia, pluralism and tolerance has always been in our DNA.”

He dismissed the idea that Indonesia faced a growing threat from foreign fighters returning from the battle front in Syria or Iraq, following the defeat of Islamic State.

“No, no. We are the largest Muslim country in the world, Indonesia. We have 220 million Muslims in Indonesia. I think if there’s only one, two or three people do this, it is very small, it is very small. We are modern Muslims, tolerant Muslims, moderate Muslims compared with other countries,” he said.

ANU professor Michael Wesley cautioned that ASEAN was an organisation that dealt in consensus but President Jokowi’s comments were “a significant development".

“While Indonesia is the biggest country and the leader of ASEAN, he would have a harder job to convince other countries, Singapore and Malaysia in particular, that Australia would form a useful part of ASEAN.”

“Geo-political and economic trends are bringing Australia and ASEAN together in much more powerful ways than ever before. It is inevitable and probably a little late that Australia is waking up to the importance of ASEAN.”

President Jokowi will face a presidential election in April 2019 but unofficial campaigning is effectively already under way.

He is due to choose a candidate for vice-president by August and his decision will be made against the backdrop of rising influence of more conservative Islamic theology on electoral politics in his country.

That influence saw a political ally of Mr Jokowi – the Chinese-Christian former governor of Jakarta, Basuki Tjahaja Purnama, popularly known as Ahok – jailed last year for blasphemy.

But Mr Jokowi said he believed Indonesians had learned lessons from last year and predicted Islam would not dominate the presidential campaign.

“No, now I think our people can learn from last year’s election, not only from Jakarta but also from the other regions, the other cities the other provinces. Our people can every year learn from the elections. I am sure then our politics can be more stable. In Indonesia, our constitution respects freedom of speech and freedom to form groups.”

with Amilia Rosa, Karuni Rompies