Soviet planes delivered tons of arms and ammunition to the Moscow-backed Afghan government last week and lifted Red Army troops out of Kabul at twice the usual rate, diplomats say.

At the current pace, the Red Army's withdrawal could be completed by the end of January, Western diplomats in Islamabad said Tuesday."However, for political reasons the Russians may wish to keep a military presence in Kabul up to Feb. 15," said one.

Under a U.N.-brokered accord, Moscow has pledged to remove its remaining troops from Afghanistan by that date, although Kabul's ruling Marxists have not reached a settlement with the Moslem insurgents who have battled them for more than a decade.