TOKYO, July 2 (Reuters) - Japan bond market participants expect the central bank to trim bond purchases by roughly $100 billion in the first year under a quantitative tightening (QT) plan set for release this month, according to a survey conducted by Reuters.

A Reuters survey of 19 banks, brokerages, insurers and asset managers showed they expect the Bank of Japan to trim bond buying by an average 16.1 trillion yen ($99.7 billion) in the first year.

That would translate into monthly purchases of 4.65 trillion yen, down from the current pace of around 6 trillion yen. In the second year, the respondents expect the purchase amount to fall to an average 3.55 trillion yen, the survey showed.

Combined, it would amount to a reduction of roughly 45 trillion yen during the two-year period.

Respondents of the Reuters survey were divided on how long the BOJ will keep tapering with nine projecting it to last for two years, while two thought it will end in an year. Several others thought the BOJ will keep tapering beyond two years.

A slight majority expected the BOJ to adjust the pace of tapering once a month or once every quarter, while others bet the change will happen less frequently or on an ad hoc basis.

The survey was conducted June 25-July 1.

At a policy meeting last month, the BOJ decided to announce in July a detailed plan on how it plans to reduce its huge bond buying and scale back its nearly $5 trillion balance sheet.

The BOJ said it will come up with a taper plan that kicks off in August, and covers a period of "around one to two years."

Governor Kazuo Ueda has said the amount of taper will be "sizeable," without offering details. The BOJ will hold a meeting with bond market participants on July 9-10 to collect their views, before deciding on the plan at its July 30-31 policy meeting.

After buying bonds aggressively for a decade to reflate growth, the BOJ has seen its holding of Japanese government bonds (JGB) balloon to 576 trillion yen - roughly half of total JGBs sold in the market.

Reducing the holdings is part of the BOJ's ongoing efforts to phase out its massive monetary stimulus, which also led to an end in March to eight years of negative interest rates.

($1 = 161.5700 yen) (Reporting by Makiko Yamazaki, Noriyuki Hirata and Takahiko Wada; additional reporting by Leika Kihara; editing by Lincoln Feast.)