CHICAGO, Aug 2 (Reuters) - Chicago is looking at the feasibility of bond financing as a way to stabilize funding for its four retirement systems, the city's chief financial officer said on Thursday.

The city's unfunded pension liability is $28 billion, down from $35 billion last year. That liability and chronic budget deficits have resulted in low credit ratings and high borrowing costs.

"I'm at a point where I feel like we need to look at (options) seriously and see whether or not there is a financing plan that would meet the kind of objections the mayor would have, our (city) council would have, the rating agencies would have," CFO Carole Brown told reporters.

Her comments followed an annual conference Chicago held for bond investors that included a presentation by Michael Sacks, chairman and chief executive of GCM Grosvenor and a member of Mayor Rahm Emanuel's economic council.

Sacks raised the idea of securitizing about $950 million of city revenue to raise $10 billion for pensions, boosting the funded ratio to 54 percent from the currently low 26 percent.

Brown said she would look to the most-cost effective financing model, noting the current model was Chicago's Sales Tax Securitization Corp, which has been able to issue higher-rated debt by giving investors a statutory lien on the city's share of state sale taxes.

Over the past 20 years, issuance in the U.S. municipal market of taxable pension bonds peaked at $17.8 billion in 2003 and totaled only $1.56 billion last year, according to Thomson Reuters data.

During the conference, the mayor fielded investor questions on the impact of Trump administration policies on the city, as well as public safety and fiscal transparency.

Emanuel ran through a litany of improvements in the city's finances, including a shrinking projected budget gap and actions taken to boost pension funding and end reliance on shaky fiscal practices such as raiding reserves.

"We have never taken a challenge and punted," Emanuel said.

(Reporting by Karen Pierog; Editing by Peter Cooney)