I'd suggest making it a wrapped class. So...
class listcontainer
{
public List<String> command;
public String ID;
}
then your web service
public String invoke(listcontainer request)
or something like that. I'd suggest always writting WSDL first. It gives you the best flexiblity and control for defining this stuff. Assuming your using SOAP, Document wrapped Literal is my preference for interoperability