By David Lawder

WASHINGTON (Reuters) - The world is swimming in a record $152 trillion in debt, the IMF said on Wednesday, even as the institution encourages some countries to spend more to boost flagging growth if they can afford it.

Global debt, both public and private, reached 225 percent of global economic output last year, up from about 200 percent in 2002, the IMF said in its new Fiscal Monitor report.

The IMF said about two thirds of the 2015 total, or about $100 billion, is owed by private sector borrowers, and noted that rapid increases in private debt often lead to financial crises.

While debt profiles vary by country, the report said that the sheer size of the debt could set the stage for an unprecedented private deleveraging that could thwart a still-fragile economic recovery.

"Excessive private debt is a major headwind against the global recovery and a risk to financial stability," IMF Fiscal Affairs Director Vitor Gaspar told a news conference. "Financial recessions are longer and deeper than normal recessions."

While the United States has de-leveraged since the 2008-2009 financial crisis, the report cited the buildup of private debt in China and Brazil as a significant concern, fueled in part by a long era of low interest rates.

The report comes as IMF managing director Christine Lagarde is urging the Fund's 189 member governments that have "fiscal space" - the ability to sustainably borrow and spend more - to do so to boost persistently weak growth.

The Fund's call for targeted fiscal support for consumer demand comes is accompanied by calls for continued accommodative monetary policy and accelerated structural reforms aimed at boosting countries' economic efficiency.

If a major deleveraging of private debt were to occur, the IMF report recommends that fiscal policy should include targeted interventions to restructure private debt or repair bank balance sheets to mininize damage to the overall economy.

These could be similar to the mortgage restructuring programs undertaken by the United States during the crisis or the Obama administration's automotive industry restructuring,

Gaspar said.

"These types of policies could be particularly useful in China," Gaspar said. "But in order to work, they need to be adequately designed and subject to strong governance principles."

(Reporting by David Lawder; Editing by Marguerita Choy)