Thanx again for your help and your input. To complete the answer you gave, here's the complete code for fixing this issue. In my situation I have put the latest version of the jquery-1.4.2.min.js in the document library that also contains the advanced.aspx.
But be welcome to put in in any library of your choice. In the code underneath I make a reference to this jquery-1.4.2.min.js. BTW, always use the minified version in a production environment.
On the advanced.aspx page I have put a hidden Content editor webpart. In the source editor I put the following code, which results in setting the 'contains' operator as the default value:
$("select[Title='Inclusion Operator'] option[Value='Contains']").attr("selected", "selected");
This does the trick!
Skudoes to Marc for you quick responses and help. I really like Jquery :-)