By Ercan Gurses and Gulsen Solaker

ANKARA (Reuters) - Turkey's ruling AK Party will soon bring to parliament its plans to expand the powers of the presidency, Prime Minister Binali Yildirim said on Tuesday, paving the way for a referendum which the nationalist opposition said it would not oppose.

President Tayyip Erdogan has long wanted an executive presidency, a Turkish version of the system in the United States or France, saying the country needs strong leadership. His opponents fear the change would mean growing authoritarianism.

"We in the AK Party will bring to our great parliament our proposal containing constitutional change and the presidential system," Yildirim told reporters in Ankara, before a meeting of the AKP in parliament.

Asked when, he said: "As soon as possible".

The government said last week it would revive efforts to change the constitution after the Nationalist Movement Party (MHP), the smallest of the four parties in parliament, indicated it would not oppose a national vote on the issue.

That announcement helped send the lira currency to a record low as investors worried about renewed political uncertainty in a country which has held four nationwide elections in the last 2-1/2 years.

"The MHP is in favor of the continuation of the parliamentary system but also does not see a problem in asking the people their view," MHP leader Devlet Bahceli said in a speech to his party's lawmakers.

"If the AKP brings its plans to parliament and takes into account our principles and sensitivities, I believe a reasonable outcome will be achieved."

Bahceli has made clear he will let deputies from the MHP, which has 40 seats in parliament, vote freely on the question of constitutional change, meaning they could back the AKP plans.

Any constitutional change requires the support of at least 367 deputies in the 550-seat assembly to pass directly, and of 330 deputies to go to a referendum. The AKP has 317 seats.

Yildirim said the government would seek a referendum on the executive presidency however much support it won in parliament, describing it as "the greatest reform to open the locks and undo the knots in the system".

"Everyone should put their personal ambitions and party interests to one side," he said.

The two biggest opposition parties, the secularist CHP and the pro-Kurdish HDP, both oppose an executive presidency and some opinion polls have shown a majority of Turks do not want the change.

But Erdogan has ridden a wave of patriotism since an abortive coup failed to oust him on July 15, consolidating both his power and popularity. A poll two weeks after the attempted putsch showed him with two-thirds approval, his highest ever.

(Writing by Daren Butler and David Dolan; Editing by Nick Tattersall and Catherine Evans)