Wilshire Real Estate Investment Trust Inc. said it offered to buy Imperial Credit Commercial Mortgage Investment Corp. for $11.33 a share in stock, a 26% premium to its current price. The offer values West Los Angeles-based Imperial Credit at about $592 million, including about $202 million of debt. Portland, Ore.-based Wilshire said it would be willing to pay as much as 20% of the purchase price in cash. In Nasdaq trading, Imperial Credit shares rose 6 cents to $9 before trading was halted; Wilshire shares fell 50 cents to $12.25 before trading was halted. Wilshire said it notified Imperial Credit's management of the offer in a Sept. 11 letter and that Imperial has "not, as yet, expressed a willingness to negotiate."