TOKYO, March 13 (Reuters) - The longest-dated Japanese

government bond (JGB) yields fell on Wednesday ahead of an

auction of 20-year securities the following day.

Overall, though, the market was quiet as investors weighed

the odds of an exit from ultra-easy stimulus at the Bank of

Japan's (BOJ) meeting next week.

The BOJ will likely offer numerical guidance on how much

government bonds it will buy upon ending negative interest rate

policy (NIRP) and yield curve control (YCC), to avoid causing

market disruptions, sources told Reuters, with analysts and

investors expecting that to happen either at the two-day meeting

ending next Tuesday or at the following gathering in April.

An end of YCC is likely to coincide with an exit from NIRP,

the sources said.

"The leaks in the media are having an impact," Shoki Omori,

chief Japan desk strategist at Mizuho Securities, said.

"Investors think something is going to happen in March -

whether it's an end of NIRP or just a tweak in ETF

(exchange-traded fund) buying - but it's very unknown," keeping

investors largely on the sidelines, he added.

The central bank uncharacteristically made no ETF purchases

on Monday despite local shares dropping sharply, stoking

speculation that a shift away from ultra-supportive policy is

imminent.

At the same time, BOJ Governor Kazuo Ueda toned down his

optimistic tone on the economy on Tuesday, acknowledging

"weakness" in some recent data.

Meanwhile, a decline in so-called superlong JGB yields is

likely position adjustments ahead of Thursday's auction, after

Tuesday's five-year note sale garnered solid demand, Omori said.

The 10-year JGB yield was flat at 0.765% as

of 0440 GMT, while the 20-year JGB yield fell 0.5

basis point (bp) to 1.530% and the 30-year yield

eased 1 bp to 1.810%.

The two-year and five-year yields

were both flat at 0.195% and 0.375%, respectively.

Benchmark 10-year JGB futures fell 0.02 yen to

145.45.

(Reporting by Kevin Buckland; Editing by Mrigank Dhaniwala)