BUDAPEST, NOV. 3 -- Warsaw Pact countries reached agreement today on how to divide up their conventional weapons, removing the last obstacle to the signing of a 34-nation European arms reduction treaty in Paris later this month.

The agreement sets ceilings on the number of tanks, aircraft and artillery pieces that each member of the Warsaw Pact can deploy under the terms of a treaty drawn up by the Conference on Security and Cooperation in Europe. The United States warned that it would boycott the Paris conference beginning Nov. 19 if the six countries of the Soviet-led pact failed to agree on a shareout.

Outstanding differences on the allocation of tanks and artillery were settled by Warsaw Pact foreign ministers on the basis of a bargaining session between military experts in Prague last weekend.

No details were announced, but pact sources said the Soviet Union would field 13,150 of the 20,000 tanks allocated to the Warsaw Pact under a U.S.-Soviet agreement in Vienna. The remainder would be shared among Hungary, Romania, Bulgaria, Poland and Czechoslovakia.

The Western NATO alliance will also be allowed to station 20,000 tanks in Europe.

The signing of the Budapest agreement was delayed by several hours while the ministers drafted an agreement on the allocation of 3,500 Warsaw Pact tanks, which the CSCE treaty will allow to be held in reserve.