Police here are investigating the possibility that Sunday's explosion at Narita Airport was caused by baggage from Vancouver intended for transfer to an Air-India flight for Bombay.

An Air-India spokesman here said that two men with the same names as two Sikh extremists wanted by the FBI for attempting to assassinate Indian Prime Minister Rajiv Gandhi during his U.S. tour earlier this month had seats on both flights but may not have used them.

Japanese police confirmed that the name "L. Singh" was on the passenger list of the Canadian Pacific Airlines Boeing 747 that had arrived from Vancouver 40 minutes before the baggage room explosion at Narita. But they said there was no record of his entry into Japan, and they could not confirm that the name of the other fugitive, Ammand Singh, was on the passenger list. One police source said that Ammand Singh had canceled his booking before the flight.

The reports here added to speculation that the Narita Airport explosion, which killed two baggage handlers, was linked to the midair destruction of Air-India Flight 182 off the Irish coast 55 minutes later, in which all 329 passengers and crew are presumed dead.

Investigators in Canada, from which both flights originated, Ireland, India and Japan were continuing to sift through the evidence, and some cautioned that it was far too early to draw any conclusions. But in Ottawa, authorities said privately that they believe the incidents were connected and that they were centering their investigation on the activities of Sikh exiles who are naturalized Canadian citizens, living principally in the Vancouver area and connected with the extremist Sikh Student Federation.

Here in Tokyo, the Air-India spokesman said, "Lal Singh and Ammand Singh made bookings in Vancouver on June 20 to fly to Tokyo with Canadian Pacific last Sunday and to take our Bombay-bound flight from Tokyo on the same day."

Speculation has emerged here that a time bomb was checked in baggage aboard the Canadian Pacific flight in Vancouver with the intention that it would explode after being transferred here to Air-India Flight 301, bound from Tokyo to Bombay. A Japanese police investigator said Sunday's explosion took place in a part of the baggage room normally used for transferring luggage to other flights. Reportedly, 44 of the Canadian plane's 374 passengers were making connections to fly on from Narita.

Canadian Pacific has not released the passenger list of its Flight 003 from Vancouver, and an airline spokesman said the list had been turned over to Canadian investigating agencies. The airline also has refused to comment on reports that six passengers had checked in for the flight but had not boarded it.

Canadian authorities are attempting to determine whether there was any connection between the two airplane incidents and an organized ring of Sikh extremists based in New York. U.S. Attorney Raymond Dearie of New York's Eastern District said that investigators there had not been able to determine whether Lal Singh and Ammand Singh had even been in Canada, but "it's something we're investigating."

A Canadian investigator, however, said he had information that the two had entered Canada illegally "very recently" and were believed to have met with Sikh extremists in Vancouver.

In Washington, FBI spokesman Lane Bonner said the bureau was continuing its search for Lal Singh and Ammand Singh but added, "We still have no basis for the report that these two fugitives were involved" in Sunday's aircraft incidents.

The two men and a third man, Gurpartap Singh Birk, who was later arrested, met three times between January and early May with an FBI informant whom they apparently had unwittingly sought out for heavy weapons training, acquisition of plastic explosives and aid in setting up a hit team to kill Gandhi.

According to an affidavit filed in support of the fugitive warrant in New York, the FBI videotaped some of the meetings between the conspirators and the informant, identified as a former Navy Seal in Vietnam and a Congressional Medal of Honor winner. The Indians told him that they wanted to smuggle explosives into India so that they could blow up bridges and high-rise buildings.

U.S. authorities moved quickly on May 10 to arrest Birk and five others in New Orleans and indict them on charges that they were plotting to kill Bhajan Lal, chief minister of the Indian state of Haryana, who was in the Lousiana city to receive medical treatment.

Dearie said he believed it was "quite a possibility" that Sunday's disasters might have stemmed from an effort to smuggle explosives into India. Canadian authorities, however, indicated that they were still pursuing leads on the theory that both explosions were acts of sabotage aimed at blowing up Air-India planes.

Mahendrasinhji Chudasama, the airline's public relations manager in New York, said he been told that Royal Canadian Mounted Police were studying the possibility that sabotage of the Air-India flight may have occurred with inside help. Sensitive X-ray equipment the airline was using to examine checked baggage broke down on Saturday night in Toronto as luggage was being processed for Flight 182.

During questioning in the Canadian House of Commons today, Transport Minister Donald Mazanowski said that efforts were being made to beef up airport security, but he and Deputy Prime Minister Erik Nielsen were guarded about details of the investigations.

[A jumbo jet bound for Venice, Italy, with 476 persons aboard was halted at toronto as it was preparing for takeoff, after a telephoned bomb threat was received, Reuter reported. But no explosives were found aboard Wardair Boeing 747].

In cork, Ireland, officials investigating the Air-India disaster said it still was too early to know whether the crash was caused by a bomb. But B.K. Bhasin, the chief Indian investigator, told reporters that "it looks quite obvious that the aircraft broke up in the air."

Bhasin said, however, that "it is too harsh to say whether anyone did it deliberately or not, so unless we can get some definite proof we cannot tell."

Irish officials said that only about 2 percent of the plane's structure had been recovered from the Atlantic Ocean, into which it plummeted from an altitude of 31,000 feet while en route from Montreal to London for refueling before going on to New Delhi and Bombay.

The Irish government issued alerts today to those along the coasts of Britain, France and Spain to be on the lookout for bodies and pieces of wreckage that may wash up from the crash.

According to an official count, 131 bodies were recovered by the multinational air and sea search that largely ended last night. Of those, 84 are listed as adult females, 13 as adult males, 16 as "girls" and 18 as "boys."

Most of the pieces of the plane that have been picked up have been relatively small, the largest an eight-foot wing section. They have been taken to the Irish naval base in Haulbowline, near Cork, for initial examination by technical experts. They then will be examined by the team of technical experts headed by the Indian government with representatives from Britain, Canada and the United States.

Bhasin, the Indian investigator, said the fact that some seats and cushions from the plane were recovered intact was an indication that the plane had broken up in midair. "If the whole aircraft had hit the water, there would have been a lot more twists and turns in the seats and other equipment," Bhasin said.

Additional pathologists were called in today to Cork Regional Hospital to aid in identifying and examining the bodies of the victims for evidence of an explosion aboard the aircraft.

A special sonar-equipped vessel, the Gardline Locater, was en route to the crash site to begin exploration for the plane's two "black boxes," flight recorders with taped records of cockpit conversation and technical readings.

U.S. sources said the recorders were thought to be 6,000 feet underwater, well below the Gardline Locater's normal operating depth. There were unconfirmed reports that the United States was making available a Glomar ship capable of recovery efforts at that depth.

"Nothing has ever been recovered from these depths before," Irish investigator Gerry McCabe said. "It is a unique problem."

The British Press Association said that the international police organization Interpol had been called in to aid efforts to identify the victims, most of whose bodies were badly fractured.