Criimi Mae Inc., the Rockville commercial mortgage company that went into Chapter 11 bankruptcy protection last year, filed a $900 million reorganization plan yesterday that envisions paying back creditors in a mix of cash and IOUs.

The plan, filed in U.S. Bankruptcy Court in Greenbelt, fleshes out the company's announcement earlier this month that New York investor Leon Black's Apollo Real Estate Advisors would provide capital to help Criimi refinance.

Criimi was the nation's biggest investor in the riskiest part of real estate loan investments known as mortgage-backed securities. It was pushed into bankruptcy court during last year's autumn credit crunch.

Criimi's stock closed yesterday at $2.12 1/2, unchanged in New York Stock Exchange trading.

The reorganization plan by management may not be the final word on Criimi's future. In a ruling earlier this month the bankruptcy judge left open the unusual possibility that creditors and stockholders could file a competing plan by Oct. 16, and other parties could file their own after that.

In recent court hearings, representatives of the creditors said they would negotiate with Criimi and Apollo to see if they can reach a plan everyone can agree on. They also said they would try to encourage other investors to make competing bailout proposals.

Unsecured creditors have about $215 million in claims against the company. Under the plan, they would be repaid 100 percent of court-approved claims--half in cash and half in the form of a new note promising future payment.

Some secured creditors would be paid back in cash, others in a mix of cash and notes.

Holders of Series B preferred stock would receive the same number of shares of a newly issued preferred stock.

Holders of common stock would receive the same number of new common stock, plus rights to buy new preferred stock.

The reorganization plan contemplates raising about $910 million. Of that money, Apollo would invest from $50 million to $61 million in convertible preferred stock. About $435 million would come from new debt issues, and most of the remaining $425 million would come from the sale of securities now in Criimi's portfolio.