An air search for the 329 passengers and crew of an Air-India jet that crashed into the Atlantic yesterday was called off late tonight after British and Irish rescue officials said there was no hope of survivors and little likelihood more bodies would be found.

A scaled-back sea search for floating wreckage that might help investigators will be continued, they said.

Irish officials at Cork airport, where the victims are being taken for examination, said only one body was found today, adding to the 130 recovered yesterday by British and Irish military aircraft and ships combing the area 110 miles off the southwestern Irish coast, where the plane plunged into the sea.

British Coast Guard officials coordinating the effort from Falmouth, in southwestern England, said however that search vessels were believed to have recovered an additional two bodies this evening.

Indian investigators arrived here today and met with British, Canadian and American aviation officials who will help them try to determine why Air-India's Flight 182, en route from Montreal to London, suddenly dropped out of the sky and fell in pieces from an altitude of 31,000 feet.

Widespread official and unofficial speculation still centered on a bomb aboard the aircraft. But Indian authorities and the British agencies that have organized the search at sea, have declined thus far to state unequivocally that a bomb was responsible.

This afternoon, a separate Air-India flight from London's Heathrow airport for New York was delayed for more than seven hours, when police said they received a threat against the plane, the nature of which they did not specify. Nothing was found on board during the lengthy search.

Two other aircraft also were targets of bomb threats today. A People Express flight from Los Angeles to Newark was diverted to Chicago and evacuated there, and an Austrian Airlines flight from Rome to Vienna had to return to Rome for inspection.

The delayed Air-India aircraft had arrived from India this morning carrying the Indian investigation team, as well as dozens of relatives of the victims. Air-India and the investigators, however, asked them to remain in London while the bodies are examined and possibly identified.

Callers to U.S. newspapers claiming to represent two separate extremist groups, the Sikh Student Federation and the Kashmir Liberation Front, have claimed responsibility for yesterday's Air-India crash. Other Sikh spokesmen, however, denied Sikh complicity, and there was no confirmation that the Kashmiri claim was authentic. The United States, Britain and Canada have Sikh communities of several hundred thousand.

Police in those nations, as well as Japan -- where luggage from a Canadian Pacific Airlines flight from Vancouver blew up at Tokyo's Narita Airport less than an hour before the Air-India crash, killing two baggage handlers -- are investigating a wide range of sabotage possibilities. The fatal Air-India flight originated in Toronto and picked up passengers in Montreal.

One report today from Spain said that a captain of a Panamanian-registered ship in the area of the crash had reported seeing the tail section of the plane explode and the aircraft make two loops before falling into the sea. The report was widely discounted, however, by officials who noted that at an altitude of 31,000 feet it was unlikely a plane would have been visible. Other ship captains in the area who assisted in the search noted, however, that heavy cloud cover at the time of the presumed explosion was at 15,000 feet.

The air crash investigators will focus on examination of the physical evidence retrieved from the sea, and the still unrecovered "black box" that recorded flight information and cockpit conversation aboard the plane. "Black boxes" aboard airliners are actually painted bright orange for better visibility.

The flight crew of the aircraft, which had been in routine radio contact with air traffic controllers at Ireland's Shannon Airport just minutes before it disappaared from their radar screens, issued no distress call and failed even to push an emergency activator that would have taken only seconds.

Officials here said that was the prime indication that an explosion had taken place aboard the plane. Thus the automatic flight recorders, currently believed resting under 4,000 to 7,000 feet of ocean, may provide the best confirmation of what happened.

Because the aircraft went down in international waters, the Indian government will head the investigation of the crash. But it has asked Britain's Department of Transportation accident investigation unit to lend to the search the underwater salvage expertise it has developed in North Sea oil operations.

A British survey vessel, the Guardline Locator, is expected to reach the crash site Thursday, where its first mission will be to locate the radio beacon the recorder boxes are designed to set off and maintain for a month under water. No signal from the beacon has been intercepted yet, but British sources said this was because it emitted a special frequency that ships involved in the search thus far were not equipped to receive.

Simultaneously, the Guardline Locator will conduct a survey of the seabed beneath the crash site to try and determine depth and the consistency of the bottom, where the recorders are believed to be.

Assuming the recorders are located, the depth at which they are resting will determine the method of retrieval. The ship will carry aboard an unmanned "remote-controlled submersible" that can be lowered into the sea and, with lights, television camera and electronic sensors, locate the boxes and bring them to the surface.

But the "submersible," which is connected to the ship by an umbilical cord, cannot operate deeper than 4,000 feet. Greater depth will require a manned minisubmarine that will likely not be carried aboard the survey vessel.

"We can get ahold of them easily, however," one official said. "They're in use around the country."

Still, he cautioned, "It's not that easy a job. All sorts of things affect the transmission of a beacon in water; temperature and the water itself can distort sound."

The official noted that the boxes from the Korean airliner that crashed in 1983 in waters south of Japan after being shot down by a Soviet plane never were located.

Information from the flight recorders will be assessed along with the results of pathological examinations now being conducted on the bodies of the victims, and examinations of the pieces of aircraft wreckage still being picked up.

A seven-man Indian investigation team arrived here today, headed by S.S. Sidhu, director general of the Indian Civil Aviation Authority and himself a Sikh.

Several members of the group traveled to the British military research establishment at Farnborough, outside London, to meet with aviation officials from Britain, Canada and the United States. British officials said the meeting was to determine the course of the investigation and the division of duties of the various members under Indian leadership. Under international law, the United States, where the aircraft manufacturer Boeing is located, must be part of the investigating team.

Other members of the Indian group went directly to Cork, in Ireland, where they had an initial look at the bodies and pieces of wreckage.

A number of government officials and aviation experts today explained that a minute examination of the human and aircraft remains could prove that a bomb had exploded on the plane even if the recorder boxes are not found.

The bodies have been found largely intact, with injuries consistent with a tremendous impact and little reported signs of burns that might have been caused by an explosion. But a bomb, explained former British chief accident inspector Bill Tench, "would throw very many tiny pieces . . . only millimeters in size. But they penetrate the bodies and are detectable on X-Rays."

Similar examinations, along with chemical tests, will be performed on all pieces of wreckage and luggage. Experts will then try to determine from airline records which of the victims were sitting where and try to match evidence found on both the bodies and plane parts.

In the wake of the Air-India disaster, as well as the reported threat today against the additional Air-India flight, security was markedly tightened at Heathrow.

Additional groups of relatives of the victims of the Air-India crash are expected to arrive in London Tuesday on flights from India and Canada. But the airline has cautioned that they may never be allowed to see the remains, or to take them home.

Most of the passengers aboard the flight were of Indian origin, many with Canadian passports. Many were children, traveling with parents or relatives over the school break.