IN 500 days on Tuesday, the 2024 Summer Olympics will burst into life in Paris as the teams float down the River Seine on barges in a unique opening ceremony.

The Paris Olympics and Paralympics have a lot riding on them, they involve the return of full crowds of spectators to the world's greatest sporting spectacle after the Covid-blighted Summer Games in Tokyo in 2021 and the Winter Olympics in Beijing last year.

On top of that, the spending on the Games is being scrutinised as never before, venues are focused on Seine-Saint-Denis, the poorest area in France.

And the buildup is being buffeted by the war in Ukraine and its ramifications for competitors from that country, Russia and its ally Belarus.

Here are the key issues to be resolved before the Games open on July 26, 2024:

- Will Russians take part? -

The International Olympic Committee's suggestion that it wants to find a "pathway" for athletes from Russia and its ally Belarus to take part as neutrals in Paris moved a stop closer on Friday when the International Fencing Federation said it would re-open its events to Russians.

Ukraine has reacted with fury to the prospect that its athletes will have to compete alongside their aggressors while their country is being bombed from the air and shelled by Russian tanks and has threatened to boycott the Games.

IOC president Thomas Bach has passed the decision on to the federations of individual sports, such as fencing.

Thirty countries including the United States have asked the IOC for "clarification" over how Russian athletes would be able to compete in practice.

- Ceremony plans cause concerns -

The plans to take the opening ceremony out of its traditional stadium setting and stage it on the River Seine, framed by the Eiffel Tower and other monuments, is an organisational headache and has provoked concerns from the security services.

The original plan allows for up to 600,000 spectators along the banks of the Seine but political sources say the number could be revised down.

Private security companies are struggling to recruit enough staff, begging the question of whether the army will be called in, as it was for the 2012 London Olympics.

Interior Minister Gerald Darmanin says it is "too early to say" while Etienne Thobois, the director general of the 2024 organising committee says "all scenarios are on the table".

- Transport headache -

Will the Paris transport system, which has been plagued by staff shortages and sporadic strikes in recent months, be ready to move millions of people around the city for the Olympics?

Now headed by former prime minister Jean Castex, network operator RATP is under extreme pressure.

There are serious questions about whether the extension of a key metro line to the Athletes' Village will be completed and a large shortfall in the number of bus drivers is causing concerns too.

Paris' airports, still attempting to return to full capacity after the Covid pandemic, are in a race against time to be ready for a massive influx of competitors and spectators from abroad.

- Ticket policy criticism -

The first sales phase for tickets sparked criticism from people who felt they were too expensive and resented being forced to buy tickets for minor sports if they also wanted to see popular events like athletics and gymnastics.

The organisers say the prices are in line with the London Olympics.

Chief organiser Tony Estanguet insisted the first stage had been a success "even if we understand the criticism and the frustration of some people who were not satisfied".

- Budget scrutiny -

The organising committee's budget, of which 96 percent comes from private funding, rose 10 percent to 4.4 billion euros ($4.7 billion) last year. Add to that another 4.4 billion euros for Solideo, the body tasked with building facilities, and the total budget comes to 8.8 billion euros.

Local politicians in the deprived Seine-Saint-Denis area are watching the expenditure more closely than anyone.

"When the Olympic flame is extinguished, residents here won't be asking (Paris Mayor) Anne Hidalgo, (President) Emmanuel Macron or Tony Estanguet for accountability, they'll be asking me," said the head of the area, Stephane Troussel.