By Chris Gallagher

TOKYO (Reuters) - Budapest, Los Angeles and Paris have expressed confidence in their ability to control costs as they prepare for the final phase of bidding for the 2024 Summer Olympics, unworried by steep overruns at next host Tokyo.

Top officials from the 2024 candidate cities, visiting Tokyo this week, told Reuters they were being vigilant on costs from the onset and were focusing on utilizing existing infrastructure to limit financial risk.

"It's an important thing to get right at this stage," John Harper, chief operating officer of Los Angeles 2024, said of the need to deliver in the bid a reasonable and rigorous budget.

Their preparations come as Tokyo 2020 grapples with spiraling expenses. Japanese organizers this week said overall costs could run as much as 2 trillion yen ($18 billion), almost three times initial estimates.

The International Olympic Committee (IOC) is fretting such a lofty figure could scare off future bidders, after cities like Rome and Boston dropped out of the 2024 race, and has called for a sharp reduction.

The IOC is keen for cities to embrace its "Agenda 2020" initiative, which calls for, among other things, creating a more compact Games and using a high percentage of existing venues to lower costs.

Harper called Los Angeles "Games ready today" and said it would use only existing facilities, including the UCLA campus for the Olympic village, or a handful of temporary ones.

"I think that is a huge budget risk that gets taken off the table by having that in existence today," he said, referring to the Olympic village plan.

Laszlo Vajda, vice chairman of the Budapest bid team, said the Hungarian capital would provide a new alternative as a mid-size city to host the Games after the mega cities of Beijing, London and Tokyo, noting the compact nature of its plan.

"We believe because of this proximity, cost in terms of transportation, infrastructure and urban overlay is much smaller than would be necessary for a much larger city," he said.

Paris is highlighting its status as a top cultural and tourist destination with not only sports infrastructure but strong access to public transport and high hotel capacity already in place.

"The financial impact of the Games in Paris is relatively low because of all the investment that has already been done in the past," said Etienne Thobois, chief executive of the Paris bid team.

"We're confident that we can deliver the Games on a reasonable scale."

IOC members will select the 2024 host at the 130th International Olympic Committee Session in Lima next September.

(Editing by John O'Brien)