Maryland officials spent $3,500 in an effort to persuade motorists not to wait until the last minute to get their car emission tests -- but procrastinators apparently paid little heed.

Despite advertisements that appeared in Baltimore and suburban Washington newspapers in mid-December, mammoth lines developed at nearly all the state's emission testing stations as motorists rushed to beat a Dec. 31 deadline.

Ray Salehar, one of the testing program chiefs, said officials are accustomed to long lines at the end of the month, but lines the last day of 1985 were unusually long.

"I think it's a combination of people being away and coming home and suddenly discovering it's the end of the month and they have to get tested," he said.

Salehar said the worst lines occurred at the Gaithersburg station in Montgomery County, where state police routed cars into a field to clear a two-lane road, and at the Carroll County station.

Motor Vehicle Administration spokesman Steve Horwitz said his agency "deliberately invested" in the ads to warn the 156,000 vehicle owners receiving test notices for December to have their cars tested early because "we know from experience that when the last day of the month falls on a Tuesday, we develop quite a crowd."

"We took out the ads to put people on notice. Some got the message and others apparently didn't," he said.