WRAPUP 4-S.Korea scrambles to defend sliding markets

* Minister to seek expansion of $80 billion Asia swap pool

* Won surges on intervention after biggest swing in 11 years

* Minister to meet U.S. bankers, seek support for local banks (Updates throughout)

By Yoo Choonsik

SEOUL, Oct 10 (Reuters) - South Korea scrambled on Friday to prop up its tumbling markets with the finance minister set to plead with U.S. bankers to keep credit lines open for local banks under threat from the global financial crisis.

It also called on East Asian countries to expand a proposed $80 billion currency swap deal to shelter their economies from the financial storm that investors fear is pushing the global economy into recession.

The won KRW= slumped as much as 5 percent in early trading and the main stock market index dropped 9 percent, prompting official and private-sector efforts to prop them up and restore confidence in the country's shaken markets.

"I have never seen anything like this in my 20-year financial career. This is probably the worst since the Great Depression. It is impossible to predict the bottom, and technical analysis is meaningless as panic and fears overwhelm the markets," said Jang Huh, managing director at Prudential Asset Management.

The won crashed this week 18 percent to its intraday low on Thursday -- also its weakest level in a decade -- even as officials tried to reassure investors the economy could weather the financial storm.

When it dropped sharply again on Friday, dealers said authorities stepped in to repeatedly sell dollars, sparking the currency's biggest daily swing since the height of the Asian financial crisis.

By the end of local trading, the won was up 5.6 percent on the day at 1,306.9 per dollar, and up almost 19 percent from the day's low.

DETECT SPECULATORS

Regulators told banks to submit records of foreign exchange trades so they could track down any speculators in the won, which has fallen 28 percent this year - by the far Asia's worst-performing currency monitored by Reuters News.

And indicating that major companies are being pushed to do their bit to help relieve strain on the currency, steel giant POSCO (005490.KS) announced it was selling $100 million for won on the local market and would issue a $1 billion global bond.

"It's strange that all the big guys sold their share of U.S. dollars today. Maybe the government also wanted corporate efforts in stabilising the forex markets," said Lee Won-jae, an analyst at SK Securities.

Heads of local brokerages pledged to form a joint fund to shore up the stock market and said they would refrain from selling foreign financial products to relieve won pressure.