By Elaine Lies

TOKYO (Reuters) - Poor supervision and a lack of clear authority is one reason costs for the Tokyo 2020 Olympics have soared to more than four times original estimates, the head of a Tokyo panel tasked with slashing expenses said on Wednesday.

Tokyo Governor Yuriko Koike, who took office in August, ordered a review of Olympic expenses that recommended changing three venues in an effort to rein in costs projected to hit 3 trillion yen ($28.87 billion), four times initial estimates when the city won the right to host the Games.

Attention has focused on the rowing and canoe/kayak sprint venue, originally set to take place at a new Tokyo facility, the cost of which has surged to around 52 billion yen, nearly seven times higher than the original budget.

The Tokyo review panel headed by Shinichi Ueyama, also a professor at Tokyo's Keio University, on Tuesday proposed changes that could cut as much as 50 billion yen from the total bill.

On Wednesday, he blamed a good part of the situation on a lack of clear oversight of expenses.

"There is no proper mechanism in place to manage the entire budget, a real lack of governance," Ueyama told a news conference.

Ueyama noted that while each organization involved in the Olympics had its own chief executive officer (CEO) and chief financial officer (CFO), they only oversaw the budget for their own group.

"There is nobody who has authority equivalent to a CEO or CFO as there is in a usual company, and this is a source of great concern to us," he added.

The Tokyo government, national government, Tokyo 2020 Organising Committee and the Japan Olympic Committee are all involved in pulling the games together.

At the end of September, Ueyama's panel recommended a number of cost-cutting changes, including moving the rowing and canoe/kayak sprint venue to an existing one 400 km (250 miles) north of the capital. The suggestion is opposed by Tokyo 2020 organizers and sports officials.

On Tuesday, in its final report, the panel said costs could be shaved by converting permanent facilities to temporary ones, or by scaling back plans for permanent facilities to build them more cheaply.

Shifting the rowing venues to northeastern Japan would require an outlay of 35 billion yen to bring them up to Olympic standard but officials have also touted this as helping to regenerate areas hit by the 2011 tsunami, one of Prime Minister Shinzo Abe's selling points when Japan originally won the Games.

International Olympic Committee (IOC) President Thomas Bach met with Koike last month and agreed to form a working group comprising Tokyo, the central government, 2020 organizers and the IOC to find ways to avoid wasteful spending.

The first meeting began on Tuesday and ends Thursday.

(Editing by John O'Brien)