The Federal Maritime Commission has taken one of the most crucial steps in the development of its Automated Tariff Filing Information system with the certification of software suppliers.

"This is the critical path," said Peter Neibert, director, marketing systems, American President Lines, Oakland, Calif."It's a stop button," Mr. Neibert said. If workable software isn't available, efforts to get ATFI on-line would be seriously hampered, he said.

The testing process began in December, and has extended into January.

"We have had four companies come in. Three of those companies have been certified to varying degrees," said Bryant L. VanBrackle, director, bureau of tariffs, certification and licensing at the FMC.

Tariffs are detailed lists of shipping prices plus the rules and mathematical formulas ship lines use to apply the prices to specific shipments.

Ship lines are required to file their tariffs with the FMC. ATFI's goal is to automate that process. ATFI's first use is scheduled for April 6.

Successful certification of software suppliers is essential if ATFI is to prove viable, Mr. Neibert said. Without good software, tariff filers will not be be able to get information to ATFI.

Certification by the FMC does not imply an endorsement; it merely confirms that the supplier's software has met certain agency requirements.

The three companies receiving certification to date are Data Exchange International Inc., Pittsburgh, World Tariff Services Inc., a Union, N.J., subsidiary of the Rijnhaave Group, and Transax Data, a Bridgewater, N.J.-based subsidiary of The Journal of Commerce. Mariner Systems Inc., San Francisco, is also working toward certification.

A test session for tariffs was held the week of Dec. 9-13, 1991, and the suppliers were notified of the results during the first week of January. A second test session was held last week.

Once software suppliers sell their wares, individual users also will have to go through the certification process. Not all ATFI users will have to get certification. The process applies to big, batch users using outside software.

Those who work directly with the ATFI and file information in small pieces are not required to be certified. These smaller users, however, will only account for a fraction of the tariffs filed with ATFI, maritime executives said.

FMC procedure is to test the filing software in seven different parts, one for each kind of filing that will be done, Mr. VanBrackle said.

''There is a certification for each level," he said.

Once they have certified, companies will be able to send in information in that category.

"We have been certified on three parts, and have been submitted for certification on the remaining four," during the second testing period, noted Peter Cass, president, Transax Data.

Transax Data has received approval for batch filing of rules, foreign commodity and essential terms tariffs. DXI has gained certification for all those as well as bill of lading and domestic commodity tariffs.

Mariner has focused its certification on foreign commodity tariffs, and has also worked on several other categories as they relate to that tariff, said Stan Levy, vice president, Pacific Coast Tariff Bureau, a publisher that is working with the software supplier.

"We feel like we're ready right now. We're just going through this process," Mr. Levy said.

The FMC will officially announce the results of its certification testing at the end of January, Mr. VanBrackle said.