ZAGREB, Croatia (AP) _ Reluctance by some Serb and Croat leaders to accept U.N. peacekeepers in war-torn Yugoslavia remains a key obstacle to the plan, days before expected Security Council consideration of the matter.

U.N. envoy Marrack Goulding failed in talks Monday to persuade a Serb leader in Croatia to accept peacekeepers in the enclave he controls.

On Tuesday, Croatian President Franjo Tudjman apparently also stalled over some unspecified points during talks with Goulding Tuesday night.

''There are differences in the interpretation of the peace plan,'' the Tanjug news agency quoted Goulding as saying today in Belgrade. ''A number of things still have to be done before the plan is realized.''

He arrived in Belgrade for more talks with Serbian President Slobodan Milosevic; the federal defense minister, Gen. Blagoje Adzic; and Borisav Jovic, a key Serb leader. All support the plan.

On Thursday, Goulding will head to New York ''for a very important meeting of the U.N. Security Council, after which I will either come back to Yugoslavia, or not,'' HINA quoted the envoy as saying.

Serbia and the Serb-dominated federal army have accepted the plan to deploy up to 10,000 peacekeepers in Croatia. Croatia also has largely accepted it.

The United Nations said it would not deploy the peacekeepers until a cease- fire was imposed, but a truce that began Jan. 3 has generally held.

The main obstacle has been the opposition of rebel Serb leaders in Croatia.

Goran Hadzic, leader of one Serb enclave in eastern Croatia, apparently dropped some objections in talks with Goulding Monday. But Milan Babic, head of the Krajina region in western Croatia, refused to change his mind in talks with Goulding in the regional capital, Knin.

The rebellion of some of the 600,000 Serbs in Croatia against Tudjman's government began in Knin in 1990, then escalated into all-out war after Croatia declared independence June 25.