MINEOLA, N.Y. (AP) _ Officials from houses of worship around the Northeast are calling police here for information about an unemployed church organist who admitted stealing artifacts from hundreds of churches.

Many of the callers wonder whether Oather James Blocker might have victimized them, or whether police have recovered their missing artifacts, said Detective Bernard Havern of the Nassau County Police Department.

''We are getting 30 to 40 calls a day, easy,'' Havern said Monday.

So far, none of about a half dozen items recovered have matched, he said.

Blocker, 45, is being held without bail on charges that he burglarized two churches in Woodbury, on Long Island, last year, making off with more than $30,000 worth of artifacts.

Investigators said Blocker has confessed to burglarizing as many as 500 churches and synagogues during the last decade, most in affluent communities in Massachusetts, Connecticut, New Jersey and New York City's suburbs.

Blocker apparently committed one theft a week, stealing articles such as gold-lined silver chalices and a Torah pointer. He then would sell the artifacts for $2,000 to $3,000 apiece, considerably less than their value, to someone who melted them down and resold them, Havern said.

''He said he was doing about $30,000 a year,'' Havern said. He said police could not provide a total dollar amount of the items stolen.

Blocker, a native of Roscoe, Texas, who moved to Manhattan in 1982, used his intimate knowledge of church operations to execute his thefts, authorities said.

''This case is certainly unique,'' said Lt. Leonard Rubino, commander of the Nassau burglary squad. ''We've never had anyone who concentrated solely on churches and temples. And to go on for 10 years without getting caught is just incredible.''

Blocker was arrested last June in Wayne, N.J., when a passer-by heard glass crashing in a church he had broken into. He pleaded guilty to the burglary and received a 90-day jail sentence.

A drifter he befriended in jail visited him last September at his home and fled with a chalice and other religious articles he had found in Blocker's knapsack, Havern said.

Police questioned the drifter as he tried to fence the items. The questioning led them to Blocker, Havern said.