The Palestine Liberation Organization has prevented food supplies stored in a United Nations warehouse here from reaching refugees in besieged West Beirut and southern Lebanon for the past 10 days, U.N. officials charged today.

PLO officials here, who in the past have bitterly condemned Israeli forces for periodic blockades of food and water to West Beirut, confirmed reports that they were preventing the U.N. Relief and Works Agency from removing food from its West Beirut warehouse.

A Palestinian official justified the decision on grounds that the agency wanted to send some of the food to Israeli-occupied southern Lebanon, a move that would reduce the supplies going to refugees in West Beirut.

The Vienna-based relief agency, which has helped Palestinian refugees for the past three decades, said that since July 19, the PLO has posted a five-man guard at the gate of the warehouse with orders to "prevent any UNRWA supplies from entering or leaving the warehouse without written authority from the PLO."

The result, UNRWA officials said in a statement released here and in Vienna and New York, was that "emergency relief operations . . . for some 30,000 displaced Palestinian refugees in West Beirut, and the movement of supplies from Beirut for distribution to homeless families in south Lebanon have been stopped."

UNRWA said contacts with the PLO to lift the restrictions "have met with no practical effect." It said a convoy of two trucks loaded with rice and sugar to be delivered Tuesday to refugees in the southern Lebanese city of Sidon, which is under Israeli control, had been prevented from leaving the warehouse.

"Distribution teams in West Beirut have been without flour, rice, sugar, corned beef and skim milk products to issue to displaced Palestinian refugees for over a week, and in Sidon, UNRWA teams have been deprived of the 48 tons of food supplies which were scheduled to have been delivered last week and today," the UNRWA statement said.

The PLO official argued that UNRWA had plentiful supplies available in Syria, Cyprus and Israel that could be sent to southern Lebanon. But in confirming the gist of the UNRWA communique, the official conceded that the PLO decision also was depriving some 30,000 displaced Palestinian civilians in West Beirut of UNWRA supplies, which are distributed through public and private channels.

The official invoked the week-long Israeli offensive against West Beirut--and the destruction and disorganization it has caused the PLO--to explain why the problem had not been settled early last week when it first arose.

The question of food and medical supplies to civilians in the western part of the city, under siege by Israeli forces since mid-June, has been an emotionally charged issue here. Palestinian and Lebanese officials have accused the Israelis of periodically cutting off supplies in order to pressure the PLO to withdraw from the city. Israeli officials said that they lifted a blockade on emergency supplies earlier this month for humanitarian reasons and have accused the PLO of using the issue for propaganda purposes.

In Geneva today, Israeli Ambassador Ovadia Soffer accused the leadership of the World Council of Churches of making "libelous" charges in a resolution condemning the Israeli invasion of Lebanon. The resolution accused Israel of "barring access of international humanitarian agencies to places of detention of prisoners and refugee relocation centers" and of blocking delivery of basic necessities for war victims.

In a statement, Soffer said Israeli forces had set up a "gigantic humanitarian and medical infrastructure . . . to aid the Lebanese population" and had worked closely with international relief agencies.