Goods trade, which has see-sawed since the turn of the century, will grow by 7 percent next year, up on this year's expected 6.5 percent, the economists said.
But WTO Director-General Pascal Lamy said the underlying picture was worrying and argued that successful completion of the troubled Doha Round world trade talks was needed to boost the trading system.
In the WTO's latest report on international trade, economists said the slowdown in 2005, after a boom last year when growth reached 9 percent, was partly due to declining consumer and business confidence in richer economies.
If the global economy - hit earlier in the year by soaring oil prices - recovered moderately by the end of December as widely expected, "world trade growth should accelerate to around 7 per cent in 2006," the report said.
This year's figure, based on trends up to July, continued the up-and-down of the past six years, which saw a dip to a 1 percent decline in 2001 after a 12 percent growth record in 2000, and modest growth of 3 and 4.4 percent in 2002 and 2003.
This followed several years of steady growth during the 1990s, when the average for the decade was 6 percent.
In the second quarter of 2005, the report said, goods trade picked up in the richer economies, "but available information points to significant growth deceleration in intra-Asian trade and in US imports" over the first six months.
"The steep rise in real oil prices, to their highest level in more than two decades, has negatively affected consumer and business confidence in the oil importing countries," the WTO economists who compile the report declared.
In a comment on the report, which confirmed preliminary figures for last year issued by the 148-member WTO in April, Lamy said the trend towards lower trade growth rates "is cause for some concern".
"To set us on the right course, we need to create more opportunities for trade, particularly in developing countries, and we need to adjust global trade rules to better meet the needs of entrepreneurs in 21st century," he said.