Error: "SQL*Plus statement ignored" when trying to declare variable in SQL Editor (4300951)

Error: "SQL*Plus statement ignored" when trying to declare variable in SQL Editor. This runs fine in SQL Plus.

For Example:

I run:
variable var varchar2(30);

Then I get:
15:22:34 Start Script Execution ...
15:22:34 **** SCRIPT STARTED: 8-Dec-2009 15:22:33 ****
15:22:34 variable var varchar2(30)
15:22:34 SQL*Plus statement ignored
15:22:34 **** SCRIPT ENDED 8-Dec-2009 15:22:34 ****
15:22:34 End Script Execution

The aforementioned script uses SQL Plus type command and it is not supported in SQL Navigator (this is the same behavior in Toad for Oracle as well). Please use the SQL Plus application to run non-supported SQL Plus commands. Please see the SQL Plus Commands supported list below.

(From SQL Navigator Help File)
SQL*Plus command support

The Code Editor in SQL Navigator supports the following SQL*Plus commands. Please consult Oracle documentation for details about Oracle's SQL*Plus utility.

Comment Delimiters (/*...*/)
Double Hyphen (- -)
At Sign (@)
Double At Sign (@@)
Forward Slash (/)
CONNECT
DESCRIBE
DISCONNECT
EXECUTE
REMARK