UPDATE 1-PREVIEW-Energy row may dominate EU-Russia summit

(Adds comments from Russian ambassador)

By Jeff Mason

BRUSSELS, Oct 23 (Reuters) - New proposals to block foreign companies from buying European Union energy assets look set to dominate an EU-Russia summit this week, adding tension to often strained ties between the bloc and its main gas supplier.

Russian President Vladimir Putin will meet EU leaders in Mafra, Portugal, on Friday for talks on issues ranging from Russia's bid to join the World Trade Organisation to differences over the future of Kosovo.

But recent proposals by the European Commission that would prevent Gazprom (GAZP.MM) and other foreign firms from buying up European energy infrastructure are likely to top the agenda.

The Commission proposed last month to break up big utilities that control power supply, generation and transmission.

But it inserted a clause to prevent foreign firms from buying pipelines and power grids if their home countries do not have similarly open markets and an agreement with Brussels.

"This particular approach is hardly compatible with what I perceive as the principles of open markets," Vladimir Chizhov, Russia's ambassador to the EU, told reporters on Tuesday.

European Commission President Jose Manuel Barroso has said he discussed the issue with Putin but Friday's meeting will be their first in person since the proposals were published.