If you're talking about an XML file I'm assuming you are referring to the diagnostics.wadcfg file. In this file, you simply write the LogLevel as defined in the XSD:
<xs:simpleType name="LogLevel">
<xs:restriction base="xs:string">
<xs:enumeration value="Undefined" />
<xs:enumeration value="Verbose" />
<xs:enumeration value="Information" />
<xs:enumeration value="Warning" />
<xs:enumeration value="Error" />
<xs:enumeration value="Critical" />
</xs:restriction>
</xs:simpleType>
If you need the numeric values of each level (I think this is also something you're asking), you can find them through the enum:
namespace Microsoft.WindowsAzure.Diagnostics
{
// Summary:
// Defines a standard set of logging levels.
public enum LogLevel
{
// Summary:
// Logs all events at all levels.
Undefined = 0,
//
// Summary:
// Logs a critical alert.
Critical = 1,
//
// Summary:
// Logs an error.
Error = 2,
//
// Summary:
// Logs a warning.
Warning = 3,
//
// Summary:
// Logs an informational message.
Information = 4,
//
// Summary:
// Logs a verbose message.
Verbose = 5,
}
}