Maryland state troopers will start using 200 portable, hand-held devices next month to make roadside tests of the blood-alcohol levels of drivers suspected of drunkenness, officials said yesterday.

The devices, which cost $400 each and are no bigger than a pack of cigarettes, will enable police to more accurately determine whether drivers are drunk, according to Col. Edward Evans, deputy superintendent of the Maryland State Police. Currently, officers must rely solely on their own judgment and on such tests as having the suspect walk on a straight line.

He said a small group of troopers were trained in the use of the device earlier this month. The initial 200 devices, which were bought under a $100,000 federal grant, will be in use state-wide by mid-February, he said. Another 200 units, to paid for with federal funds, are to be purchased by the end of March, Evans said.

Use of the roadside breath-testing devices was made legal last July 1 when Maryland's new drunken driving law took effect. The new law does not require motorists stopped by police to submit to the breath test and prohibits the use of the results as evidence in a trial, according to Dan McCarthy, state police spokesman.

But once drivers formally are charged with drunken driving, they are required under the new law to take a blood-alcohol test from a court-sanctioned testing device, usually located at a police station. Those who refuse to be tested lose their license to drive for 60 days.

The pre-arrest breath-testing device is in use by law enforcement agencies in the United States, Europe, Australia, New Zealand, and South Korea, according to its St. Louis, Mo., manufacturer.

In the breath test, which takes less than 60 seconds, the suspect breathes through a disposable mouthpiece, and the results appear on a lighted digital display.

"Frequently, an officer who arrests a motorist on the road must drive another 30 minutes to an hour to a station where the suspect's blood alcohol level can be tested on a chemical testing device whose results are accepted as evidence in court," said M. R. Forrester, president of the manufacturing concern.

The advantage of the device, he said, is that troopers can be certain at the roadside that the driver has a high blood alcohol level that is not likely to change by the time he gets to a more sophisticated blood alcohol test, he added.

Currently, 17 states have laws which permit the use of pre-arrest breath testing devices and four other states use them without a specific law, according to John Moulden, a research specialist for the National Highway Traffic Safety Administration.