could the u.s.govt.delay or eventually reschedule or suspend payment
of treasury obligations?maybe in effect going into a defacto ch.11
reorganization.

Yes

But if that happened the US would already be in such chaos that nobody
would even notice.

Joegar --

Treasury securities (bills and bonds) are backed by the faith and
credit of the government and the assumption has always been that in
lieu of default, the government would simply print more money.  This,
of course, leads to inflation -- but it's all part of the financial
structure of a modern economy.

Might I suggest the following Google search strategies:
"risk free rate" treasury bills
"risk free rate" treasury bonds
"risk free rate" T-bills

Best regards,

Omnivorous-GA

Yes they could, and they came surprisingly near to doing so in the
1990s when there was a political scuffle over raising the debt ceiling
(as I remember it, Rubin borrowed from a government employees' pension
fund in order to make a coupon payment).  If they did, your assumption
that it would be "like Chapter 11" is actually quite optimistic.

Unlike the corporate bankruptcy case, there is no bankruptcy code for
countries (because you can't just replace the management!).  There is,
therefore, no settled body of law about how defaulted debts are
resolved, considerable potential for conflicts of interest between
different classes of creditors and much trouble assured.  It is also
impossible to sue a sovereign entity in its own courts unless it
allows itself to be sued.  Have a look at the Russian default to see
how messy things can get.

On the other hand, it is not particularly likely ...