* PGE shares are set to rise by about 13 pct on debut - poll
* Analysts divided on quick inclusion in WIG20 index
By Patryk Wasilewski and Agata Nalecz
WARSAW, Nov 2 (Reuters) - Poland's top energy group PGE is expected to rise 13 percent when it starts trading later this week after Europe's largest listing in 2009, and could even gain enough to join Warsaw's main index this year, analysts said.
The state-owned utility's 6 billion zlotys ($2.1 billion) offer was heavily oversubscribed by both institutional and individial investors, who faced heavy reductions after they bid 45 billion zlotys.
The shares, which was priced at 23 zlotys, or the top of the set range, are set to debut on the Warsaw stock exchange on Thursday or Friday.
According to an average forecast in a Reuters poll of brokerages and banks, PGE is expected to rise 13 percent to about 26 zlotys per share. This would push PGE ahead of Pekao bank as Warsaw's largest listed company.
"I think the debut will be a success, if nothing negative happens on the market at the time," said BRE brokerage analyst Kamil Kliszcz. "I think the stock has a potential to grow by 12-20 percent, but not necessarily on the first session."
Polish media reported some local investment funds have complained they had not received any shares in the offer, which could turn them into eager buyers in early sessions.
"There should be demand from institutional investors. They must factor in the fact that PGE will join the WIG20 index in a longer perspective," said Jacek Buczynski, analyst at Deutsche Bank in Warsaw.
Analysts were almost evenly divided on PGE's prospects of joining the index this year,.
The extraordinarily quick inclusion would require the value of PGE's free float to exceed 5 percent of the value of companies already in the index.
According to estimates by BZ WBK brokerage, the stock would have to rise by 24 percent and hit 28.5 zlotys in order to meet the criterion.
Inclusion in the index would allow funds that track the main Polish index to invest in the stock, supporting its share price. Expectations of PGE's eventual inclusion helped support the offering.
PGE is Poland's largest producer, generating 42 percent of its energy, and needs to fund extensive modernisation of outdated and heavily polluting coal-fired generators as well as Poland's first nuclear power plant.
The PGE offer also has gained in significance because of the government's need to curb its budget deficit during the slowdown and after Poland failed to reach a deal to sell its controlling stake in utility, worth some $3 billion, to Germany's RWE.
Poland's treasury will only indirectly receive funds from the sale, mainly through dividends.
The issue is managed by Unicredit CAIB and Goldman Sachs (Additional reporting by Pawel Bernat; Editing by David Cowell)