KUALA LUMPUR, Malaysia - Even as they celebrated the discovery of underwater signals that possibly came from Malaysia Airlines Flight 370, the authorities involved in the search cautioned Monday that they were still far from confirming the location of the airliner and solving the mystery of its disappearance.

The Australian naval vessel the Ocean Shield, equipped with technology on loan from the U.S. Navy, picked up a series of electronic pings Sunday that had the characteristics of transmissions from a plane’s data and cockpit voice recorders, commonly known as black boxes.

But on Monday, officials said the ship had been unsuccessfully trying to locate the signals again as it slowly swept a remote section of the Indian Ocean, hundreds of miles northwest of Perth, Australia.

Personnel from the U.S. Navy who are operating the underwater detection equipment on the Ocean Shield were hoping to achieve more “signal detections” to be able to pinpoint the source of the pings, said Cmdr. William Marks, a spokesman for the Navy’s 7th Fleet, which is overseeing U.S. naval participation in the search. But the process is slow and deliberate.

At the same time, the batteries in Flight 370’s black boxes are expected to expire this week. The closer to expiration, the weaker the pings are.

Locator beacons on the black boxes have nonrechargeable lithium batteries. The power cells like those on Flight 370’s pingers usually last three to five days longer than the 30-day specification at full signal power, according to manufacturer Dukane Seacom. Today marks exactly one month since the flight disappeared.

Warren Truss, Australia’s acting prime minister while Tony Abbott is overseas, said today that the crew on board the Ocean Shield will launch an underwater vehicle, the Bluefin-21 autonomous submarine, today to search for the black boxes.

The unmanned miniature sub can create a sonar map of the area to chart any debris on the sea floor. If it maps out a debris field, the crew will replace the sonar system with a camera unit to photograph any wreckage.

“Today is another critical day as we try and reconnect with the signals that perhaps have been emanating from the black-box flight recorder of the MH370,” Truss said. “The connections two days ago were obviously a time of great hope that there had been a significant breakthrough, and it was disappointing that we were unable to repeat that experience yesterday.”

If the plane’s black boxes are found, the effort will become a recovery operation. At such depths, that could take “a long, long time,” measurable in months, said Angus Houston, the retired Australian Air Force chief who is the lead coordinator of the search.

“This is not the end of the search,” Houston said during a news conference in Perth on Monday. “We’ve still got a lot of difficult, painstaking work to do.

“In deep oceanic water,” he said, “nothing happens fast.”

Despite all the uncertainties, the authorities heralded the series of underwater signals as a possible breakthrough in the search for the plane, a Boeing 777-200 with 239 people aboard.

The signals were detected Sunday about 1,050 miles northwest of Perth, officials said.

The signals picked up by the Ocean Shield occurred over the course of about 5½ hours late Sunday in the northern part of the current search zone, northwest of Australia, officials said.

The Ocean Shield is outfitted with a so-called towed pinger locator, a batwing-shaped device that is towed behind the vessel, deep in the water, and can pick up signals from the black boxes’ beacons. The locator is towed at no more than about 3½ mph and has a range of about a mile. In addition, turning the ship around and resetting the locator can take several hours each time.

The sensors first detected the signal - a series of consecutive pings at one-second intervals - in the late afternoon and held it for more than two hours, officials said. The ship lost contact, turned around and picked up the signal again for about 13 minutes, officials said. On the return leg, sensors detected pings coming from two different locations, suggesting transmissions from both black boxes.

Detecting a pinger signal for more than two hours suggests that what the Ocean Shield picked up was more than a false alarm, said John Fish, a principal at Bourne, Mass.-based American Underwater Search & Survey Ltd. who has been involved in several efforts to find aircraft that crashed in oceans.

“That speaks volumes,” Fish said. “That is exactly what you would expect to find.”

False signals tend to be shorter in duration and difficult to replicate, he said. The fact that the ship detected it a second time also indicates that it may be nearing the crash site, he said.

Officials said that determining the nature and source of the signals might take several days, and that there was still no proof of the plane’s whereabouts.

The frequency used by aircraft flight recorders, 37.5 kilohertz, was chosen because no other devices use it, and because nothing in the natural world mimics it, said William Waldock, a search-and-rescue expert who teaches accident investigation at Embry-Riddle Aeronautical University in Prescott, Ariz.

“They picked that so there wouldn’t be false alarms from other things in the ocean,” he said.

But these signals are being detected by computer sweeps, and “not so much a guy with headphones on listening to pings,” said U.S. Navy spokesman Chris Johnson. So until the signals are fully analyzed, it’s too early to say what they are, he said.

“We’ll hear lots of signals at different frequencies,” he said. “Marine mammals. Our own ship systems. Scientific equipment, fishing equipment,things like that. And then of course there are lots of ships operating in the area that are all radiating certain signals into the ocean.”

While U.S. Navy Capt. Mark Matthews said the signals picked up by the Ocean Shield were both 33.3 kilohertz, the manufacturer indicated the frequency can drift in older equipment.

The Malaysia Airlines plane disappeared March 8 after it veered off its scheduled route to Beijing from Kuala Lumpur, and vanished from civilian and military radar.

The focus of the search changed repeatedly since contact was lost with the plane between Malaysia and Vietnam. It began in the South China Sea, then shifted toward the Strait of Malacca to the west, where Malaysian officials eventually confirmed that military radar had detected the plane.

An analysis of satellite data indicated the plane veered far off course for a still-unknown reason, heading to the southern Indian Ocean, where officials say it went down at sea. They later shifted the search area closer to the west coast of Australia.

In Malaysia, Hishammuddin Hussein, the country’s defense minister and acting transport minister, said Monday that the announcement in Perth had made him “cautiously hopeful.”

“We have been through a real roller-coaster ride based on leads that we have received,” he said. “But as usual, some leads are much more positive than others.” He added, “I would like everybody to continue to pray.”

Also Monday, the British ship HMS Echo was using sophisticated sound-locating equipment to determine whether two separate sounds heard by the Chinese patrol vessel Haixun 01 over the weekend were related to Flight 370. The Haixun detected a brief “pulse signal” on Friday and a second signal Saturday.

The Chinese reportedly were using a sonar device called a hydrophone dangled over the side of a small boat - something experts said was technically possible but extremely unlikely.

China’s official Xinhua News Agency reported late Saturday that the signal detected by the Haixun crew was pulsing at 37.5 kilohertz.

Meanwhile, the search for any trace of the plane on the ocean’s surface continued today. Up to 14 planes and as many ships were focusing on a single search area covering 29,954 square miles of ocean, 1,400 miles northwest of of Perth, with good weather predicted, said the Joint Agency Coordination Center.

The director of the International Air Transport Association said Monday that he wants to see a globally agreed upon tracking standard in place by the end of this year, which also takes into consideration the cost on airlines, in order to avoid another disappearance.

Tony Tyler told a small media gathering in Abu Dhabi, United Arab Emirates, at the Global Aerospace Summit that the cost of tracking will have to be examined in any decision.

“Clearly cost is one of the issues that will have to be considered when we are looking at what to do about it. And we have to make sure that what we do is something that the airlines can afford,” Tyler said.

The association has 240 member airlines carrying 84 percent of all passengers and cargo worldwide.

Tyler said that regulation must be driven by the United Nations’ International Civil Aviation Organization.

Information for this article was contributed by Kirk Semple, Chris Buckley, Keith Bradsher, Michael Forsythe, Nicola Clark, Michelle Innis and Matthew L. Wald of The New York Times; by David Fickling, Michael Sin, Kyunghee Park, John Walcott, Alan Levin, Shamim Adam, Jason Scott, Phoebe Sedgman, Laura Hurst, Zachary Tracer, Michael Heath, Edward Johnson, Andrea Rothman and Thomas Black of Bloomberg News; and by Allen G. Breed, Nick Perry, Eileen Ng, Rohan Sullivan, Kristen Gelineau and Aya Batrawy of The Associated Press.

Front Section, Pages 1 on 04/08/2014