NEW YORK, June 16 (Reuters) - Bond investors head into Kevin Warsh's first policy meeting as Federal Reserve chair this week with a far more cautious posture, reflecting a rapid shift in market expectations and heightened uncertainty about the direction of monetary policy.

The U.S. central bank's Federal Open Market Committee is widely expected to keep its benchmark overnight interest rate in the 3.50%-3.75% range at the end of a two-day meeting on Wednesday, as policymakers weigh the possibility that the Iran conflict will keep inflation elevated.

Portfolio managers and strategists were notably more guarded than at the start of the year. What began as an expectation for easing under a new Fed chair has shifted toward a market that is now pricing in a more hawkish policy path, after a run of stronger-than-expected labor data and sticky inflation resulting from higher oil prices fueled by the Middle East war.

U.S. and Iranian officials said on Sunday they have agreed on a peace framework for a deal to end their war and reopen the Strait of Hormuz, likely leading to lower energy prices once oil shipments resume through the critical waterway.

U.S. rate futures are now pricing in a 64% chance of a rate increase by the December meeting. That marks a sharp shift from a month ago, when the odds of a December hike stood at just 24%.

For the Fed, however, the outlook is far from straightforward. Warsh has taken the helm amid expectations from President Donald Trump that he will use his influence to push FOMC members toward cutting interest rates, adding a layer of political pressure to an already uncertain policy environment.

Given that tension, the bond market has largely stepped back from bold directional bets, instead favoring a more neutral duration stance and a tilt toward higher-quality fixed-income debt. Duration measures the interest-rate sensitivity of a given bond holding.

Dan Siluk, head of global short duration and liquidity at Janus Henderson, said, "People with a longer duration focus like those in the institutional community are moving down the curve a little and just parking in that front end where you get less price volatility," meaning they are buying more short-term debt.

Shorter-duration bonds allow investors to capture yield without taking on significant capital risk.

The latest Treasury Client Survey from J.P. Morgan showed that short duration positioning from the bank's active clients rose to 33%. Neutral positioning in Treasuries has also increased for a third straight week to 58% among J.P. Morgan's all clients group, highlighting the cautious mindset.

"The unknowns don't warrant concentrated duration," said Matthew Steinaway, chief investment officer of Global Fixed Income Solutions at State Street Investment Management.

"Warsh is facing a lot of unknowables. You've got his public statements around the need for change on the committee and his objective here is to not instill high-level market volatility on day one."

DEFENSIVE STANCE

The bond market's neutral repositioning also reflects a broader defensive tilt across portfolios. Investors are reducing duration, avoiding the long end of the Treasury market in favor of shorter and intermediate maturities, where yield is still attractive but volatility is lower.

Several managers said portfolios are still biased toward investment-grade credit, but in a more selective, low-risk way.

In general, investors anticipate that the Fed will signal a shift to a neutral policy bias in its statement before embarking on a hiking cycle even as actual rate increases are still some way off. That said, a segment of the market continues to expect interest rate cuts next year.

"There are growth concerns toward the second half of this year and we don't feel that with the Iran war, inflation right now has improved growth prospects," said George Catrambone, head of fixed income, Americas at DWS.

These concerns are also shaping expectations around how the Fed communicates its policy stance. Warsh has said previously that he is not keen on forward guidance and favors less communication on policy intentions.

Some investors see the possibility of a longer-term shift in Fed communication tools, such as less-frequent forward guidance and a softer role for the so-called "dot plot" of interest rate forecasts -- though there are doubts whether we'll see a big shift this week.

"Warsh would risk undue volatility by coming out too direct and too definitive on what his plans are, particularly after just one meeting with his colleagues," said Janus Henderson's Siluk.