The General Assembly has adopted a budget by consensus for the first time in more than 40 years, and the fiscal plan includes financial reforms backed by both the United States and Soviet Union.

The United States responded to Wednesday's action by paying nearly $30 million of the more than $500 million it owes in back dues to the world body, a U.N. official said.The budget adopted Wednesday allocates $1.76 billion for 1990 and 1991, about $22 million less than the revised figures for the 1988-89 budget. It does not include funds for several special peacekeeping operations.

"In real terms, what is happening is staff is being reduced, so personnel costs are going down, and all other costs are being held at zero growth," said U.N. financial spokesman Fred Eckhard.

U.S., Soviet, Japanese and Western European officials sought a 15 percent U.N. staff reduction. The world body has cut 12 percent.