please, explain me the difference in following examples:

1. ...there was an enormous growth in popularity of Olympic games with a steady increase both in the number of SPORTS INCLUDED and the number of COUNTRIES PARTICIPATING.

2. ...contributions from all the PARTICIPATING NATIONS.

I never know, when I shall place the adjective before the noun and when behind the noun in sentences like this. Is there any grammatical rule for it or is it just a matter of style? Why is the adjective in sentence 2 before the noun? In other words, would it be incorrect if I would say in the sentence 1: ...the number of INCLUDED sports and PARTICIPATING countries?

Thanks for your answer!
You are very observant! Unfortunately there are no rules to determine which participles can be used attributively. Some can, some can't.

The number of included sportswouldn't be what people normally say, and what people don't normally say is unidiomatic at best and ungrammatical at worst!Emotion: smile (I know that's not idiomatic English, but I like it!)

The countries participating is interchangeable with the participating countries. The countries participating is actually what is considered a relative clause equivalent in some countries: [the] countries [that/which were] participating.

Anonymousanother one cannot (e g *a found object)
I don't disagree with the major thrust of Swan's message, but this is an unfortunate example in my opinion. I accept "a found object" as completely grammatical.

Students: Are you brave enough to let our tutors analyse your pronunciation?
See: Practical English Usage by Michael Swan - entry: participles used as adjectives.

The author writes: "It is not always easy to explain why one participle can be used before a noun (e g a lost dog), but another one cannot (e g *a found object). This is a complicated area of English grammar which has not been completely analysed."
 CalifJim's reply was promoted to an answer.
Students: We have free audio pronunciation exercises.

I must admit this question puzzles me too. I think you can only postpone an adjective if it is derived from a verb form ie a past participle or a present participle, for one thing. Then SPORTS INCLUDED is sort of short for SPORTS WHICH ARE /HAVE BEEN INCLUDED. Whereas when you use INCLUDED SPORTS you define the sports as such ,just as you would say winter sports for example.

I am not too sure about this explanation and I'd love to read more about the question!