They also expect reassuring moves by rating agencies and regulators and a possible change in tone from major foreign holders of U.S. debt, such as China, could limit bond price declines. U.S. yields should also be capped by an extended period of near-zero interest rates and purchases by the Federal Reserve, they said.
Not everyone is sanguine on the possible market reaction to a default.
"It's more complicated than saying people would get their money back eventually," said Geoffrey Lunt, senior product specialist for fixed income at HSBC. "If it was a company, you would be very concerned indeed, even if you think they will eventually pay," he noted.
"There are institutions and individuals who rely on those coupons being paid. I appreciate there are contingencies," on prioritizing certain payments, he said. "But I'm not sure just saying, well, you'll get your money back eventually, is the same as saying there's no issue at all."
(Read more: Debt default damage already unfolding)
In a recent note, Nomura said it also didn't believe the market would take a default, however temporary, in its stride. "The consequences of this scenario would most likely be extreme and just the sheer fact of getting closer to it may have serious market implications, even if the risk seems remote," it said, although it noted it believes this scenario is unlikely.
"If we approach the point where the debt limit becomes binding without a clear path to raising it, money markets could be disrupted as institutions hoard cash to cover event risk and in general markets as investors reposition portfolios toward safe assets causing an imminent inflection point in risk markets," Nomura said. "A U.S. default on interest and principal would limit the infusion of cash flows into the market, potentially triggering contagion," it said.
"A drawn out delay of payments could echo a 'Lehman-like' event in the sense that money markets would be so extremely affected."
(Read more: How a US debt default could hit your finances)
To be sure, Capital Economics does have some caveats to its view. It doesn't expect a default to spur significant, paradoxical, safe-haven demand for Treasurys. While the 2011 budget standoff resulted in safe-haven Treasury demand, the euro zone was still in crisis then, it noted. "Many investors could, and surely would, turn to alternative safe havens."
In addition, "having defaulted once, the U.S. government might find it had to pay a higher yield on its debt than otherwise for the foreseeable future," the note said.
—CNBC.Com's Leslie Shaffer; Follow her on Twitter