How to do > and < in execquery

Trying to check for open service orders. 
This works, but checks for only one status. 

<root xmlns="http://astea.com.schema.bc.service_order">
  <session email="" alias="">
    <state bc_name="service_order">
      <action name="execquery">
        <attribute in_var="" out_var="" entity_name="order_locator" query_name="order_locator_scrl"
                   sort_column_direction="+" sort_column_alias="request_id"/>
        <attribute dtype="argument" name="where_cond"
                   value="(serial_no = '3090R720141') and (order_stat_uniq_id = 100)" operator="="/>
      </action>
    </state>
  </session>
</root>

I want to check for < 500, but it does not parse as valid xml.
Any ideas?

<root xmlns="http://astea.com.schema.bc.service_order">
  <session email="" alias="">
    <state bc_name="service_order">
      <action name="execquery">
        <attribute in_var="" out_var="" entity_name="order_locator" query_name="order_locator_scrl"
                   sort_column_direction="+" sort_column_alias="request_id"/>
        <attribute dtype="argument" name="where_cond"
                   value="(serial_no = '3090R720141') and (order_stat_uniq_id < 500)" operator="="/>
      </action>
    </state>
  </session>
</root>