GENEVA (AP) _ A report released Thursday by U.N.-appointed investigators said the number of people disappearing after arrest or abduction is rising and urged governments to speed up inquiries into the ''wicked'' human rights violation.

The report on ''involuntary disappearances,'' presented to the United Nations Human Rights Commission, cited new cases in El Salvador, Guatemala, Peru and Sri Lanka. It also singled out Argentina and the Philippines.

Argentina showed the largest number of outstanding cases with 3,345. The report said 26 new cases dating back to 1973-80, partly during military rule, were uncovered last year.

Involuntary disappearances are ''still increasing in proportion to the population in affected areas,'' the report said, labeling them ''one of the most wicked violations of human rights.''

It said families of missing persons have increasingly ''become targets of harassment and ill-treatment'' or murder, and that there is also a rising number of disappearances of people serving jail sentences.

The report cited about 100 new disappearances over the first five months of 1985 in Peru, where the government is fighting leftist Shining Path guerrillas.

Evidence indicates most of the disappearances came during a ''counter- insurge ncy campaign undertaken by the various branches of the armed forces and the police since the end of 1982,'' said the report.

But ''a number of people listed as missing may in reality have enrolled with Sendero Luminoso (Shining Path) voluntarily.''

In the Philippines, 212 people disappeared between January 1984 and May 1985, including three children, the report said.

Some of the missing may now be connected with groups opposed to the government and several were last seen taking part in large demonstrations, it said.

The annual report, the sixth under a commission mandate, was compiled by a five-member working group headed by Ivan Tosevski of Yugoslavia and is based on testimony from relatives, witnesses and human rights and church groups.

In Sri Lanka, the report listed 194 new cases in the first five months of 1985. One mass arrest involved 99 people and a government official reportedly doubted that any survived, it said.

The report said that in over 100 cases, Sri Lankan authorities either denied arrests or gave wrong information on prisoners' whereabouts.

It cited 179 disappearances last year in Guatemala, part of 552 cases since 1980 uncovered for the first time.

''In one case the person had been kidnapped from a hospital and in 10 cases the persons had been summoned to a military barracks or had entered police offices and subsequently disappeared,'' the report said.

Reports from El Salvador alleged 11 new disappearances last year and an additional 285 in 1977-81 of which the group was informed only last year. Involved in the alleged arrests and abductions were armed forces, national guardsmen and police, the report said.

Basic legal procedures in El Salvador ''had to some extent proved ineffective and, therefore, could not be considered a genuine safeguard against arbitrary detention,'' it said.