UPDATE 1-Deadline passes for GM bondholders; focus now on Ch. 11

* Bondholders had until 5 p.m. EDT/2100 GMT to take deal

* GM had no comment

* GM expected to file for bankruptcy on Monday (Adds expiration of GM bondholder deadline; Obama administration reaction to GM, Opel deal)

By Poornima Gupta and Kevin Krolicki

DETROIT, May 30 (Reuters) - General Motors Corp on Saturday finished a key piece of business before a bankruptcy filing planned for Monday as the deadline for bondholders to accept an exchange offer brokered by the Obama administration expired.

GM would not comment on how many investors had expressed support for the debt-for-equity swap that would give them up to 25 percent of a reorganized company in exchange for $27 billion in bond debt.

Bondholders had until 5 p.m. EDT/2100 GMT to register their support for the deal, which would give them up to 25 percent of a reorganized GM.

The new, sweetened deal for the bondholders -- a 10 percent stake in the reorganized GM and warrants for another 15 percent stake -- already had the support of investors representing at least 35 percent of GM's bonds.

Fund managers and analysts said it was possible that the bond offer could have attracted a majority of the GM bond investors by the deadline.