OTTAWA, Mar 10 (Reuters) Nortel Networks Corp. , one of the world's largest telecommunications equipment suppliers, said on Friday that it would delay filing its 2005 annual report until April 2006 and restate results from certain prior periods to fix accounting mistakes.

Nortel, which was already working to repair damage from a previous accounting scandal, said preliminary fourth-quarter 2005 results show a net loss of $2.2 billion and revenue of $2.9 billion. The quarterly loss includes a $2.5 billion litigation expense.

Preliminary results for the full-year 2005 show a net loss of $2.4 billion and revenue of $10.8 billion.

Nortel, which is the subject of U.S. and Canadian criminal and regulatory probes for earlier accounting trouble, said it expects changes to its results for 2003, 2004, and the first nine months of 2005. It will also need to adjust periods before 2003, largely due to revenue recognition mistakes.

The adjustments were found during a contract review and audit of 2005 results.

Nortel said it expects the revisions to negatively impact 2003 revenue by $157 million and earnings by $91 million, and its 2004 revenue by $77 million and earnings by $93 million.

For the first nine months of 2005, the restatement will negatively impact $162 million in revenue and $95 million in earnings.

In financial results prior to 2003, Nortel expects revisions to negatively impact revenue by $470 million and earnings by $99 million.

''This revenue is real - it was recognized in the wrong periods,'' said chief executives Mike Zafirovski in a statement.

Nortel also said on Friday it will target operating margin expansion in excess of $1.5 billion in 2008, as part of a short-term plan to build shareholder value.

($1=$1.16 Canadian) REUTERS SY HS1908