By Kirk Semple

New York Times News Service

KUALA LUMPUR, Malaysia — As the intensive hunt for Malaysia Airlines Flight 370 entered its second month Tuesday, the only certainty was that it would become the most expensive search and recovery effort in aviation history, with an international fleet of ships and planes scouring the Indian Ocean at a cost of millions of dollars a day.

For the most part, the dozens of countries that have contributed personnel, equipment and expertise to the search have borne the costs while declining to disclose them, with officials offering a united front in saying that it would be callous to talk about money while a commercial airliner and the 239 people aboard remained unaccounted for.

Early today, officials reported that an underwater signal had been detected on two occasions the day before, reviving hopes that they still might locate the Boeing 777-200’s data and voice recorders. Still, many of the governments involved may soon face a tough decision about whether to keep bearing the extraordinary costs of the search, analysts said.

“Each country will have to ask itself: What are the prospects of further investigation and the cost-benefit of it?” said Ramon Navaratnam, chairman of the Centre for Public Policy Studies at the Asian Strategy and Leadership Institute in Kuala Lumpur. “If there’s no prospect, there’s no prospect: We have to be very realistic. But it’s a very difficult to decision to make. It’s like someone on a medical support system and you have to determine whether to pull the wires or not.”

Until now, the costliest search and recovery effort ever undertaken followed the crash of Air France Flight 447 hundreds of miles off the coast of Brazil in 2009, reaching about 115 million euros, roughly $160 million at the time, over the course of two years, according to estimates by experts who participated in that effort.

But the search for Flight 370 is already far more complicated, and may have already topped that total. Some of the ships involved cost hundreds of thousands of dollars a day apiece to use, and some of the aircraft being used can cost thousands of dollars an hour each to operate, officials say.

While there is an international convention that determines responsibility for air accident investigations, there are no protocols or treaties that dictate who pays, experts said. The most likely case is that the countries and companies participating in the search for Flight 370 will bear their own costs, several analysts predicted.

Even if searchers are able to pinpoint wreckage from the plane soon, it would open another costly chapter, involving undersea exploration and possibly the recovery of parts of the plane, bodies and other evidence from depths of nearly 3 miles.

Angus Houston, an Australian who is the lead coordinator of the search, said that the recovery phase could in itself take “a long, long time,” measurable in months.

In the case of Air France Flight 447, the French agency that investigated the crash, the Bureau of Investigations and Analysis, spent about 32 million euros on the undersea search and the forensic investigation of debris.

The airline and the plane’s manufacturer, Airbus, together ended up covering about 16 million euros of those costs. The costs of the search were shared by the governments involved, including France, the United States and Brazil, which was also responsible for conducting autopsies of 50 of the passengers.

“At times this is done by specific states, and at others on a joint basis,” said Anthony Philbin, spokesman for the International Civil Aviation Organization, a U.N. group.

In the past few weeks, after the search for the missing Malaysia Airlines jetliner shifted to the southern Indian Ocean, the burden has been shouldered largely by a seven-nation coalition: Australia, China, Japan, Malaysia, New Zealand, South Korea and the United States. Those countries together have contributed at least 10 military vessels, one polar supply vessel, 14 military aircraft and five civilian aircraft, officials said. At least seven merchant ships from various nations have also participated, and in recent days, Britain has added a naval survey vessel and a nuclear submarine.

But those numbers do not account for the contributions when the search ranged from the South China Sea to the Strait of Malacca and included many more nations, scores of planes and ships, and hundreds of personnel.

Among the countries involved in the current phase, only the United States and South Korea have publicized their expenditures.

The Pentagon spent about $3.3 million to cover the cost of U.S. ships and aircraft participating in the search through the end of March. The Pentagon has also budgeted an additional $3.6 million to cover search costs, including the deployment of the underwater device that detected potential beacon pings over the weekend, said Lt. Col. Jeff Pool, a Pentagon spokesman.

During the first three weeks of South Korea’s involvement, which began March 15, the government spent about $563,000 to cover the operation of a P-3C Orion surveillance plane and a C-130 Hercules transport plane as well as food and other expenses to support 39 pilots and other personnel, according to a spokesman for the country’s Foreign Ministry.

And with as many as a dozen aircraft flying daylong reconnaissance flights, the aerial search alone is costing hundreds of thousands of dollars per day.

In addition, millions of dollars have been spent on radar and satellite data collection, as well as on the criminal investigation of the pilots and others aboard Flight 370.

Some analysts do not expect much haggling, however, about the final costs of the search.

“I don’t think a lot of these countries are big on heaping the bill on Malaysia,” said Oh Ei Sun, a senior fellow at the S. Rajaratnam School of International Studies in Singapore. “It’s just not the right thing to do.”