I wanted to chime in as there have been some ridiculous comments and clearly incorrect information.
First, the issue with reciprocal rights does not mean that the US would be allowed to discriminate based on nationality (or ethnicity etc). The original poster clearly wants the US to discriminate based on nationality.
Legal residents (green card holders, or people with work visa identifying they are doing patent work) can become patent agents or patent attorneys here. I agree that it is up to Congress to decide if work visas should be given to foreigners in this area (in practice this may be difficult, as many are not H1-visa holders but instead may be e.g. internal transfers inside a company from one country to US using different visas etc). It is not up to USPTO to start discriminating based on nationality (in fact, supreme court struck down the previous state bar requirements of US citizenship).
I also wanted to correct Isaac:
"There are tough requirements to becoming a EPO Patent Attorney, but they apply to Europeans and Americans equally."
This is not true. Only Europeans (nationals of member states of European Patent Office) can become European Patent Attorneys. Non-citizens are not allowed. On the other hand, if you are a foreigner and have been living in a EPO country for some time and fulfill the formalities (degree, 3 years of OJT under qualified European Patent Attorney etc), then the president of EPO can make an exception and allow you to take the exam. I don't know how common this is.
Each EPO country has different requirements (I think most require citizenship) if you want to practice as a local patent agent in Europe. European Patent Attorney status allows you to practice before EPO, but local country agent/attorney status are still needed to practice before national patent offices. Of course, you don't necessarily need both.
For non-Europeans, the biggest hurdle is probably the language. At least for European Patent Attorney tests you need to to understand two languages (e.g. english and german/french) and also the exam is much more difficult than patent bar here (I think pass rate is around 15%).