June 21 (Reuters) - Financial markets need to consider the risks of relying heavily on the dollar-based London Interbank Offer Rate (Libor) because this reference rate could stop being published, Federal Reserve Governor Jerome Powell said on Tuesday.

"Market participants are not used to thinking about this possibility, but benchmarks sometimes come to a halt," Powell said in prepared remarks in New York for a roundtable discussion on a report on alternative reference rates.

Libor is one of the world's most important benchmarks and about $300 trillion in contracts reference Libor, Powell said.

But Libor has come under scrutiny since traders at several large banks were accused of rigging daily Libor rates.

That scrutiny has led to requirements that banks base their submissions for Libor rates on actual market trades, which Powell said was made difficult by a long-term decline in the money market borrowing that underlies U.S. dollar Libor submissions.

"It is difficult to ask banks to submit rates at which they believe they could borrow on a daily basis if they do not actually borrow very often," Powell said.

(Reporting by Jason Lange in Washington; Editing by Diane Craft)