Maryland Transportation Secretary William K. Hellmann, hoping to ease traffic congestion on I-270, plans to add new lanes to the commuter-clogged highway months ahead of schedule and has earmarked an "unprecedented" amount of state money to widen Rte. 28, a key feeder road to the interstate, officials said today.

Hellmann is scheduled to release here on Friday a final construction schedule for the I-270 project that accelerates by at least one year the widening of portions of the interstate from near Montrose Road to near Clarksburg Road, according to officials familiar with the plan. That area extends from south of Rockville to north of Gaithersburg.

Hellmann could not be reached for comment today but Robert McGarry, Montgomery's transit chief, said he was "grinning from ear to ear" about the prospect of speeded construction.

State transportation officials recently told the county that a shortage of highway engineers threatened to delay the widening of I-270 until after 1989, the year when the state was scheduled to add two high-speed lanes and four access lanes to the 16-mile stretch of the road.

County officials say the $125 million widening project is the single most important road improvement needed to spur development along the high-technology corridor and ease the daily traffic snarls on Montgomery's major north-south commuter route.

Last month, Baltimore Mayor William Donald Schaefer lent to Hellmann's department a city highway planner who has long dealt with federal transportation officials, a move that should go far toward accelerating construction, officials said.

Hellman also plans to announce on Friday that the state will spend $3 million to $4 million to improve a two-mile stretch of Rte. 28 between Rockville and Quince Orchard Road, officials said. The money will come from a special projects fund normally used for relatively minor and less costly traffic improvements.

One Montgomery official described the special fund expenditure as "unprecedented" for its size and the speed with which the state is expected to issue it.

The widening of Rte. 28 from two to four lanes could begin as early as this summer, McGarry said.