By Fumbuka Ng'wanakilala

DAR ES SALAAM (Reuters) - A former U.N. deputy secretary general has joined the race to be the Tanzanian ruling party's presidential candidate, setting her sights on becoming the country's first woman president.

Asha-Rose Migiro joins more than 30 other candidates from the ruling Chama Cha Mapinduzi (CCM) party. Numbers have been swelled from the usual dozen or so by the perception that President Jakaya Kikwete standing down leaves a more open field.

The CCM has ruled since independence in 1961, and whoever wins its nomination on July 12 is all but certain of taking office after Kikwete.

"Working with the U.N. and being at different leadership positions in my country has imparted me with experience and exposure...I am looking forward to deliver the best leadership," Migiro was quoted as saying by the Citizen newspaper.

A CCM spokesman said Migiro had picked up presidential nomination forms at the ruling party's headquarters on Monday.

Migiro did not respond to Reuters requests for comment.

Tanzania's foreign affairs minister before becoming deputy U.N. chief in 2007, she is seen as one of the Kikwete's closest allies. That ministry is a traditional stepping stone to the presidency, with two of four presidents having held the post.

Kikwete is standing down this year after a maximum two terms. He said in a statement on Tuesday that he has not picked a successor, saying the unprecedented number of CCM presidential candidates was a sign of democracy.

Former prime minister Edward Lowassa and incumbent foreign affairs minister Bernard Membe are seen as front-runners in the presidential nomination race.

Other notable candidates include Vice President Mohamed Gharib Bilal, Prime Minister Mizengo Pinda, former Speaker Samuel Sitta and Makongoro Nyerere, son of the country's first president, Julius Nyerere.

Analysts said the fractious opposition would struggle to mount a credible challenge despite plans to field a single presidential candidate in the Oct. 25 election. Parliamentary and local government elections will take place on the same day.

While ruled by a single party for more than half a century, Tanzania has seen peaceful transitions to different presidents since multi-party politics returned in 1995.

(Editing by Drazen Jorgic and Louise Ireland)