SOFIA/BRUSSELS (Reuters) - Bulgaria is considering nominating Kristalina Georgieva, the EU commissioner now in charge of sorting out the bloc's budget in the face of Britain's planned departure, for the U.N. Secretary-General job.

Officials and diplomats in Sofia, Brussels and elsewhere told Reuters there were intensive talks on Georgieva joining the race for the top U.N. job and a final decision was expected in the coming days. Ten people have already declared their candidacy.

Bulgaria's Deputy Prime Minister Rumiana Bachvarova, asked whether Bulgaria would nominate Georgieva, said:

"It is a decision of the prime minister and he will consider the situation. Consultations with other countries are also needed for a such a decision. For the moment there is no official proposal tendered at the government. If there be such, it can be tendered by the end of the working day on Monday."

South Korea's Ban Ki-moon will step down from the top U.N. job at the end of the year and former Portuguese prime minister Antonio Guterres, who also served as the U.N. High Commissioner for Refugees, has been the frontrunner so far.

Bulgaria's own candidate, Irina Bokova, who is director-general of U.N. cultural organization UNESCO, has polled equal third.

Officials differed on whether she would have to quit the race to allow Sofia to nominate Georgieva, whether Bulgaria could have two candidates or other countries could propose the Bulgarian EU commissioner.

In Brussels, Martin Selmayr, the influential head of cabinet of the Commission's head, Jean-Claude Juncker, said on Twitter: "Would be great loss for @EU_Commission. But Kristalina would make strong UNSG, and many Europeans proud. + strong signal for gender equality."

Civil society groups and nearly a third of the 193 U.N. member states have pushed for the first woman secretary-general.

Georgieva has been discussed as a potential candidate earlier in the process but Sofia eventually put forward Bokova, who was not immediately available for comment on Sunday.

The next secret ballot for the top U.N. job -- the fifth such vote -- is due on Sept. 26 and a diplomatic source in Sofia said Georgieva may have the backing of Hungary, Croatia and Latvia. But the person stressed it would be odd for Sofia to have others nominating a Bulgarian national.

"The Bulgarian prime minister is in a very difficult situation... Seems he has not decided yet," the source said of ongoing talks, which also include Bulgaria's ruling center-right GERB party.

To be successful, any candidate must be endorsed by all five veto-wielding, permanent members of the U.N. Security Council - Russia, China, France, Britain and the United States.

The German and Hungarian government spokesmen declined to comment, as have the spokespeople for the Bulgarian and Latvian foreign ministries.

But the Latvian said that the leaders of Latvia, Lithuania, Portugal, Malta and Cyprus were due to dine with the German Chancellor Angela Merkel in Berlin later on Sunday.

The German leader could play a big role in pushing Georgieva's case, something the Russian foreign ministry said Merkel has already attempted.

"Not so long ago, on the sidelines of the G20 summit in Hangzhou (China), the German chancellor tried to discuss with Russian leaders a possible support by the Russian side of a Bulgarian candidate - different from the officially nominated one," Russia's state-owned TASS news agency on Sunday quoted the ministry's spokeswoman, Maria Zakharova, as saying.

(Reporting by Tsvetelia Tsolova in Sofia, Alastair Macdonald in Brussels, Gergely Szakacs in Budapest, Gederts Gelzis in Riga, Michelle Martin in Berlin, Writing by Gabriela Baczynska; Editing by Stephen Powell)