Those deficiencies range from the government's failure to present expert testimony on the validity of the test results to an inability to show that the machines are in compliance with Massachusetts regulations.

"Most judges say the prosecution needs a witness from the Office of Alcohol Testing to bring in the records and testify to their authenticity," said Braintree lawyer Russell J. Matson, whose practice consists primarily of OUI defense. "A lot of judges will find that unless [the government] has an expert on retrograde extrapolation, they're not going to let the numbers from the breath-test machine in."

Matson said he spoke to an official at the Registry of Motor Vehicles "and he thinks that between half and two-thirds of the breath-test results are not going in at trial. I've certainly had a bunch of cases myself where it's the day of trial and the DA's Office knows they haven't got enough to go forward on the breath test."

While declining to state a percentage, Plymouth County District Attorney Timothy J. Cruz acknowledged that members of the defense bar have had success challenging the admissibility of breath-test results.

"I think the legislative intent was clear that expert testimony and witnesses from the OAT were not required, but at this point it's going to be up to an appellate court to make a determination," Cruz said. "I would hope they would do that sooner rather than later, so we can get some definitive results on this."

It appears that determination may come next month in the context of two Franklin County cases joined for oral argument at the Supreme Judicial Court on Feb. 8.

The cases — Commonwealth v. Colturi and Commonwealth v. Thomas — raise the question of whether a retrograde extrapolation expert is necessary in order to admit breath-test results. The cases do not address the issues dealing with the OAT witnesses.

In the meantime, Matson and other OUI lawyers report that the prosecution has not had OAT or expert witnesses available at trial unless a case involves a fatality or serious bodily injury.

As a result, potentially damaging readings from the breath test have been deemed inadmissible, thus increasing the likelihood of a not-guilty verdict.

"With the most damaging piece of evidence no longer in the picture, it goes without saying that the case certainly becomes easier to defend," said George Hassett of Quincy.

And since the breath-test evidence can be so damaging and is no longer refutable at trial, lawyers note they have had no choice but to vigorously fight its admissibility.

"If you get to the point where a determination is made that the evidence is in, it's much more difficult to try the case because judges are instructing jurors that the readings are per se evidence of being under the influence," said Reynold A. Ilg of Lowell. "That can be difficult to overcome, but fortunately those results haven't been coming in on a regular basis."

When they do come in, and the number is significantly above the limit, Concord attorney David J. Burgess agreed that the judge's instructions are tough to contend with.

"If the goal was to make it easier to get a conviction in those cases where a judge deems the evidence admissible, then I think they've succeeded in doing that," he said.

DA Cruz noted that while the law was also designed to encourage pleas and move cases more quickly through the system, the increased motion practice in OUI prosecutions has thus far frustrated that goal.

"There is no doubt that some judges have been keeping these important results from being introduced at trial, and I think they, too, are probably looking for some guidance," Cruz said.

As far as whether an OAT representative has to be available in order to authenticate breath-test records, Cruz said it would be extremely difficult to have someone present to testify at every Massachusetts OUI trial

"I'm not sure how many keepers of the records there are for the OAT, but it would be completely impractical to bring someone in for every trial when you think about the fact that there are 14 counties in the commonwealth of Massachusetts and 350 some-odd communities," he remarked.

A spokesperson from the OAT did not respond to a telephone call or e-mail request for comment.

One District Court prosecutor, who asked not to be identified, called the situation "a mess" and identified the limited resources available at the OAT as a major source of the problem.

"You can't cut people in half and make them be in more than one place at a time," the prosecutor said. "But there are some judges who have essentially taken the position that if there's no expert or no one there from the Office of Alcohol Testing, then it's excluded."