(Combines trade and inflation, updates throughout)

* June exports -2.7 pct y/y (Reuters poll: -8.3 pct, May exports -6.0 pct)

* Exports fall at slowest pace since June 2015

* June CPI +0.8 pct y/y (Reuters poll: +0.8 pct)

* Government working on stimulus package

By Christine Kim

SEOUL, July 1 (Reuters) - South Korean exports fell for an 18th straight month in June, and though the pace of decline was the slowest in a year, the potential impact on world growth after Britain's messy divorce from the EU has analysts urging caution over the outlook.

The external risks have already prompted Seoul to unveil an $8.7 billion stimulus package as Asia's fourth-largest economy struggles to pick up momentum in the face of weak exports and consumption.

Shipments from the world's sixth-largest exporter fell 2.7 percent in June from a year earlier to $45.3 billion, the smallest decline since June last year, data from the Ministry of Trade, Industry and Energy showed on Friday.

"It's premature to be too optimistic right now as global uncertainties will persist in the wake of the Brexit vote. I doubt exports will turn positive by year-end," said Park Ok-hee, an economist at IBK Securities in Seoul.

"China may see momentum softening in the second half of the year, so this may just be temporary," she added.

Britain's vote last week to leave the European Union sparked a two-day selloff in global markets, and despite a semblance of calm in the past few days analysts and policy makers are worried about the longer term impact of Brexit on global trade and growth.

South Korea's imports dropped at a faster 8.0 percent pace to $33.7 billion, producing a record trade surplus of $11.6 billion.

A Reuters survey had forecast exports to have fallen 8.3 percent in June and imports were seen down 9.5 percent.

The average export value per working day was $1.97 billion in June, higher than the average value of $1.85 in May, the data showed. June's average working day export value was the largest since September last year.

To shore up the sputtering economy, the government will move a supplementary budget worth around 10 trillion won ($8.68 billion) to parliament soon. The finance minister has said the supplementary budget should be ratified before mid-July.

The Bank of Korea last month unexpectedly cut interest rates for the eighth time in its current easing cycle to bring the base rate to a record low 1.25 percent, and some analysts are forecasting another cut in coming months to spur growth.

The BOK is also expected to trim its GDP growth forecast of 2.8 percent for this year at a quarterly review in July.

Earlier on Friday, data showed consumer prices rose 0.8 percent in June on-year, steady from May.

($1 = 1,151.8900 won) (Reporting by Christine Kim; Additional reporting by Dahee Kim; Editing by Shri Navaratnam)