EXPORTS rose 19.8 per cent last month over January last year, kicking off 1993 with an another strong surge that economists say could top last year's robust 20.8 per cent growth. The depreciation of the yuan, coupled with a recovery of sorts in the United States, will oil the way for a continued push of re-exports from China through Hongkong, economists say. S.G. Warburg chief regional economist Enzio von Pfeil said: ''A continued, even if somewhat bumpy, recovery in the US suggests that things will continue bubbling along quite nicely. ''We think the yuan will continue to fall, so we can still sell cheaply into these third markets, despite recession, because these goods are still quite competitive.'' Figures from the Census and Statistics Department released yesterday show imports grew 13.3 per cent last month from a year earlier to $63.35 billion. Retained imports slid 4.7 per cent. A government spokesman dismissed this as a December bottle-neck of import shipments ahead of the Lunar New Year. But at Peregrine Brokerage, senior economist Vincent Chan linked the slide in retained imports to a slowdown in retail sales, which were partially tailing off on the back of a drop in car sales from unsustainable levels early last year. The slim margin of exports over imports gave Hongkong a visible trade surplus of $374 million. Last year, Hongkong posted a $30.34 billion shortfall and in January 1991, the tally stood at a $2.73 billion deficit. But the one-month slip does not signal a sea-change, economists say - the amount involved is small and represents only one month. Re-exports rose 26 per cent over a year earlier to $49.16 billion and domestic exports nudged up 2.8 per cent to $14.56 billion. Mr von Pfeil was encouraged by the marginally higher growth in domestic exports, but Mr Chan pointed out that technical factors were at play - the comparable figure for January 1991 showed a fall of 26 per cent and created a lower base. Mr Chan said: ''It seems domestic export growth is still on a downturn, and I don't think there will be much recovery on this front.'' Re-export figures also contained some technical distortion, as the same month in 1991 was again weak, he added.