* Financial watchdog chief suggests announcement on Sunday
* Limits to apply to forwards, currency swaps, NDFs
* Focus on grace period for banks to adjust
By Yoo Choonsik and Cheon Jong-woo
SEOUL, June 11 (Reuters) - South Korea's government is likely to announce on Sunday new rules on currency trading that will apply to a range of trades and derivatives with the aim of making the won less volatile, officials said.
Planned caps on currency forwards will also cover cross-currency swap trades as well as non-deliverable currency forwards, an official at the financial regulator said.
The watchdog's chief later all but confirmed that the new rules would be unveiled on Sunday. "You'd better not make any appointments on Sunday," Chin Dong-soo told reporters.
The authorities, alarmed by the won's sharp swings in turbulent markets, have been priming investors for weeks for action aimed at reducing volatility and short-term foreign debt.
According to government sources, the new rules would focus on banks' currency forwards and the most likely scenario would limit domestic banks' positions half of their equity, with the cap set at 250 percent for foreign bank branches, which typically have much lower capital.
The won closed 0.4 percent higher and South Korean cross-currency swaps stabilised on Friday after a slide earlier this week, in a sign that markets have largely discounted the news.
Analysts said markets will now focus on how much time banks will be given to conform with the new rules.
"If it is short and banks have to unwind their positions rapidly then the new rules would exacerbate rather than reduce market volatility," Standard Chartered Bank said in a note.
Among possible scenarios mooted by government sources is a three-month delay with which the new rules would come into force and then banks would be given additional two years to meet the new limits, which analysts say should help to calm market nerves.
LOPSIDED MARKET
Authorities believe the won is more exposed to markets' gyrations than most Asian peers because of a high proportion of short-term foreign debt.
The debt, equivalent to 60 percent of the nation's currency reserves and 40 percent of total foreign liabilities, largely reflects an imbalance in the forward market caused by heavy dollar selling by shipbuilders and other big exporters in the forwards market.
This depresses costs of dollars making borrowing the U.S. currency and swapping into won, particularly attractive.
In addition, banks need to offset long dollar positions in their deals with exporters with dollar borrowing, which also drives up short-term debt volumes, leaving South Korea exposed to a sudden dollar squeeze, similar to that that followed the collapse of Lehman Brothers in 2008.
Korean authorities estimate that on average foreign banks forward positions amount to 250-300 percent of their capital suggesting that as a whole they would require relatively moderate adjustments. However, Barclays Capital estimates the figure at around 500 percent, meaning foreign banks would need to unwind positions totalling around $35 billion.
The unwinding of the forwards would also prompt some offloading of South Korean bonds and stocks by investors who use the dollar/won forwards to protect their investments against currency risk, Barclays said.
Nevertheless, JPMorgan said in a note the new rules should have limited impact mainly because banks would probably be given some time to adjust their positions.
Kim Eng Tan, a credit analyst at Standard & Poor's in Singapore said the planned controls would not affect South Korea's A rating.
"It probably will raise financing and hedging costs for some people. But I don't think it's going to be so big an increase that it will affect economic activity in a very big way," Tan told Reuters.
Tom Byrne, senior vice-president at Moody's, also ruled out any impact on ratings. Moody's rates South Korea at A1.
In November, when the authorities unveiled limits on companies' currency forwards, the won fell as investors rushed to cover short dollar positions. But the impact proved short-lived and the won, then in a rising trend, resumed its climb. The restrictions announced last year also applied to currency forwards, non-deliverable forwards, foreign exchange swaps and cross-currency swaps. (Additional reporting by Kim Yeon-hee and Kevin Yao in SINGAPORE; Writing by Tomasz Janowski; Editing by Jan Dahinten)