Top officials of Cubic Western Data, the San Diego company that manufactured the much-criticized Metro Farecard machines, said yesterday that better maintenance has dramatically improved the performance of the farecollecting equipment.

The company officials also said if Metro would spend "less than $5 million" for improved equipment Cubic has developed and tested, Farecard machine performance would be even better.

R. l. deKozan, Cubic's senior vice president and general manager, said in a press conference at the Farragut Metro station that the maintenance program ensures 95 percent of all Farecard equipment is working properly at any one time. If the improved equipment were installed, he said, the percentage would be 99.

Last summer, Metro's $53 million Farecard equipment was involved in an unacceptably high number of incidents, such as rejection of dollar bills by ticket-vending machines, or Farecards swallowed at exit gates that then refused to open. A chart displayed by deKozan showed between 60 and 70 percent of Farecard equipment was working at any one time last June, when the system was at its worst.

Metro General Manager Richard S. Page then called the Cubic Western people into his office and told them to fix the equipment. He said he was thinking of scrapping the entire Farecard system -- an option he is still seriously considering.

Metro officials, who were invited to the press conference but did not attend, said yesterday that Cubic indeed has made a major effort, in recent months, to improve Farecard performance.

But Metro quarrels with the 95 and 99 percent figures for operational equipment. Fady P. Bassily, a Metro equipment expert, said, "There is no question (Cubic's) proposed modification is a step in the right direction" . . . however "it is not enough. I think a numbers game is being played. They count differently than we do."

Bassily said Metro is developing its own numbers on availability of equipment. "There's no way they will show 95 percent availability, but I'm not sure exactly what our numbers will show yet," he said.

DeKozan said all the vending and Addfare machines at Farragut West's 18th Street entrance have been fitted with simpler, more reliable machines to accept coins and bills. Equipment has been modified to resist dirt and electrical power surges, he said.

The entrance-exit gates as well as the vending and Addfare machines have been fitted with new "transporters," the belt-and-pulley devices that accept Farecards in one slot and return them to the riders through another.

The transporter has been the Achilles' heel of the Farecard system, and this new one is the thrid Cubic has tried.

The average Farecard transporter now can handle about 1,500 to 2,000 transactions without jamming, but Metro would find acceptable a failure rate of one jam every 10,000 transactions, deKozan said.

The new transporter, deKozan said, is performing at a rate of more than 25,000 transactions between jams.

Page says he is now completing a study on Metro's subway fare structure, and is preparing long-range recommendations.

"We have no plans to buy their super-duper transport(er)," he said. "If we decide we should not buy more Farecard equipment, we should not spend more to impove what we've got. If we are going to stay with Farecard, then we need to spend the money. We will have to decide that by November," when Metro must place an order for more fare-collecting equipment.

Cubic won the Metro contract from Control Data Corp. in a proceeding that is under investigation.The U.S. attorney's office here is looking into allegations that Cubic provided gratuities to key Metro employes so they would influence the Metro board in Cubic's favor.