t's hard to decide how to take the U.S. Maritime Administration's ''new look'' report on the status of the U.S.-flag merchant fleet.

People who have followed the agency's statistical reports are used to seeing a fleet of about 350 vessels, all of them oceangoing ships or Great Lakes vessels. The radically different enumeration that was issued with much ballyhoo last week lists 37,700 vessels, most of them barges in domestic service.The abrupt change stirs conflicting thoughts.

On the one hand, Marad deserves credit for giving overdue recognition to the nation's domestic fleet. It performs needed, often overlooked functions in the nation's transportation system.

On the other hand, Marad is giving so much attention to this sector that the traditional backbone of the U.S. merchant marine - the oceangoing ships capable of carrying the nation's foreign commerce, including the kind of high-value general cargo that is usually packed into containers - is all but lost in the shuffle.

One thing that's certain is that the new format raises fundamental questions about U.S. maritime policies and programs, including the merchant marine's role in national defense. It also threatens to obscure arguments about the mission and needs of the traditional U.S.-flag fleet. And it's sure to confuse a public that is already hazy on matters maritime, a public that's likely to equate the word ''vessel'' with the word ''ship.''

Marad's traditional quarterly data sheet on the U.S. merchant marine focused on the nation's privately owned, deep-draft, self-propelled vessels of at least 1,000 gross tons. These are container ships, general freighters, tankers, dry-bulk carriers and cruise ships.

The reports have painted an increasingly discouraging picture over the years as the U.S.-flag fleet dwindled from a total of more than 4,500 ships at the end of World War II to 285 oceangoing ships and 69 Great Lakes vessels as of April 1, 1999. Moreover, any inventory these days is going to be skewed by the fact that, because of corporate acquisitions, most U.S.-flag container ships in the international trades are owned by foreign companies (though they are operated by U.S. companies and crewed by U.S. seafarers).

Meanwhile, as America's international trade has swelled on the rising tide of globalization, U.S.-flag ships have carried less and less of it. In fact, Marad's 1998 annual report shows the U.S. fleet carried only 2.7 percent of U.S. waterborne foreign commerce during the previous year; for high-value liner-trade cargo, it was slightly higher - 9.1 percent.

But there's a bigger story than international cargo, the Maritime Administration says. So its new report dramatically shifts the spotlight to virtually everything else that's American, that floats and that is commercial. And if you use the term ''vessel'' liberally, as maritime dictionaries say you can, that adds up to a lot of vessels - more than 100 times the previous reports' recent totals, in fact.

Most of the vessels in Marad's new report - 28,947 - are in the protected domestic trade. They're required by the Jones Act to be U.S.-built, U.S.-owned and U.S.-crewed.

Most of those - 24,037 - are inland-waterways barges of less than 1,000 gross tons. There are another 1,661 inland-waterway barges of more than 1,000 gross tons.

The report also lists 5,446 tugs and towboats; 1,377 oil-industry crew and supply boats of under 1,000 tons capacity; and 1,491 ''passenger vessels,'' more than 800 of which can accommodate no more than 150 passengers.

Yes, U.S.-flag vessels in the nation's foreign trade are there - there are 407 of them, 144 of which are self-propelled. But they're swamped by everything else.

Organizations representing the domestic trades cheered the new format. They said it provides a more accurate picture of both their industry in general and the increased role and number of barges in particular - including barges and integrated tug-barge combinations that are used in the oceangoing coastal trade and in ocean services to Alaska, Hawaii, Puerto Rico and Guam. The picture that emerges from the report flies in the face of conventional wisdom that the U.S. fleet is declining, they said.

Unspoken but clearly present was appreciation of the public-relations boost the new Marad report will give the domestic industry as it continues to strive against any and all efforts to tinker with the Jones Act. The controversial law perennially comes under fire as a protectionist, special-interest measure that inflates costs for shippers. The report will provide its backers with ammunition.

The rosy report will do little, however, for the U.S.-flag deep-sea sector that's been upstaged. And that's where the questions will start from a variety of quarters. Among them will be these:

Is this just a public-relations gimmick to focus attention away from a long-ailing sector that shows no sign of improvement? Will the U.S. flag be allowed to slip quietly away from America's international trades while the government focuses on river craft?

What about shippers that barges don't or can't serve?

And what about the merchant marine's proud claim to be the nation's fourth arm of defense? Through history, it's been a highly valid claim; the merchant marine's per-capita death rate in World War II was second only to that of the U.S. Marine Corps. Will a fleet in which barges provide 85 percent of the cargo capacity be able to serve America's military needs? Will the people who man such a fleet be qualified to man deep-sea vessels, as professional as they may be at their domestic jobs?

Will the government continue to support such programs as the U.S. Merchant Marine Academy? Should it? How much attention should the government pay to the maritime industry at all?

The most basic question is this: Is Marad trying to broaden the public's picture of the maritime industry, or just trying to shift the focus to a different part of it? The agency should take care. It's not wise to try to load all your cargo in one vessel.