UPDATE 1-WestLB CEO quits following disagreement with owners

* WestLB CEO steps down unexpectedly

* No immediate successor named

* Resignation follows disagreement with majority owner

(Adds details, CEO quotes)

DUESSELDORF, Germany, May 18 (Reuters) - WestLB's WDLG.UL chief executive Heinz Hilgert resigned Monday following a disagreement with the German bank's owners over how to restructure the stricken lender.

The bank did not name an immediate successor for Hilgert, who had been in office since May 2008 and whose resignation was unexpected.

His departure came with the bank in the midst of a restructuring, a vital step to consolidating the stricken German Landesbank sector.

Hilgert said his situation had become untenable after WestLB's majority shareholder, the regional association of savings banks, declined to back his restructuring proposal.

"I have laid down my role as chief executive and member of the management board of WestLB. I deeply regret this development," Hilgert told journalists at the bank's headquarters.

WestLB needs about 5 billion euros ($6.7 billion) of guarantees to help it restructure, Hilgert said.

Duesseldorf-based WestLB is seeking to transfer about 80 billion euros in risky assets off its balance sheet into a special purpose vehicle.

The proposal to offload risky assets such as troubled financial instruments tied to student loans and government bonds, was "not met with sufficient support" among the bank's owners, Hilgert said.

The savings bank's association had initially signed agreements pledging to support the restructuring before withdrawing their support for his plan, he said. The sudden withdrawal of support made no sense, Hilgert said.

Before submitting his resignation, Hilgert presented quarterly results. WestLB's first-quarter pretax profit was 250 million euros, compared with about 74 million euros a year ago. (Reporting by Matthias Inverardi, writing by Edward Taylor ($1 = 0.7422 euro)