East-West trade swelled during the first half of 1988, ending the stagnation that has prevailed since 1984, a U.N. study says.

The annual report compiled by the 34-nation U.N. Economic Commission for Europe predicts future growth as a result of Soviet-bloc market-oriented reforms and reduced international tensions.The figures showed the Eastern European satellites shifted trade away from the Soviet Union and toward the West last year. The report said that trend is expected to continue in the next few years.

"Sentiment in most Eastern countries appears to have turned again in favor of greater integration into the world economy," the study said.

Paced by Poland and Romania, Eastern European exports to the West rose 7 percent in January-September 1988, the study said. During that period, Bulgaria, Czechoslovakia and East Germany reversed export declines recorded in 1987.

Imports from the West continued a slow recovery with 3 percent growth during the same time. However, Hungary and Romania, in line with restrictive economic policies, both cut their Western exports for the second straight year.

Higher oil sales, mainly re-exports of crude from OPEC countries, sparked a 13 percent rise in Soviet exports to the West from January-September 1988, the latest period for which figures were available. Imports jumped 11 percent after a two-year fall, with Western grain shipments rising steeply.

Economic factors cited for the general rise in exports last year were continued growth in Western countries and trade-stimulating measures, such as currency devaluations by Poland and Hungary.