The U.S. Treasury is delaying a decision on whether to start borrowing in an unconventional way to help cover the federal budget deficits: By offering Treasurys with variable interest rates, like those on some home mortgages.

Treasury said Wednesday that it wants more time to study how the system would work.

It's also looking into whether start issuing debt with negative yields. Investors would, in effect, pay the government for the privilege of socking their money in ultra-safe Treasurys.

Many global investors have been shifting money into Treasurys out of fear of riskier securities, especially those linked to Europe's debt crisis. Such demand has helped drive down Treasury yields and made it cheaper for the U.S. government to borrow.

Normally, the longer the maturity on a Treasury security, the higher the yield the government must pay. But the variable-rate Treasury would let the government pay an initially low rate even while borrowing for two years or more.

Offering a variable rate would carry some risk for the government: It would have to pay investors more if rates rose, as many economists predict they will in coming years. Yet the government might consider that risk worth the benefit of attracting more investors drawn to the prospect of potentially higher yields.

The move would also reduce the need for government to hold as many Treasury auctions.

Treasury gave no timetable for its decisions. But officials said any sale of the new securities wouldn't occur before 2013 because of the time needed to prepare Treasury's computer systems. Continued...