UPDATE 3-CFTC seeking tighter controls on commodity trading

* CFTC planning summer hearing on position limits

* Analysts worry CFTC crackdown could hurt volumes

* US senator welcomes Obama's moves to get tough on market

* CME and ICE shares sink on fears of trading restrictions (Adds share prices for CME and ICE and exchange comment)

By Russell Blinch

WASHINGTON, July 7 (Reuters) - The top regulator of U.S. futures markets is considering a clampdown on excessive speculation in energy and commodity trading by restricting holdings of big players, part of a broader move by the Obama administration to stabilize the financial markets.

Commodity Futures Trading Commission Chairman Gary Gensler said in a statement on Tuesday that the agency will hold hearings in the next few weeks to seek comments from consumers and market players on whether to set position limits on all commodity futures contracts.

"Our first hearing will focus on whether federal speculative limits should be set by the CFTC to all commodities of finite supply, in particular energy commodities such as crude oil, heating oil, natural gas, gasoline and other energy products," said Gensler, who took office on May 26.

CME Group Inc (CME.O) slumped more than 5 percent to $282.06 on Gensler's statements, while IntercontinentalExchange (ICE.N) dropped more than 12 percent to $98.03 a share.