It is a few minutes after seven on a sparkling morning when Maryland State Trooper Steve Churchill steps from a grassy divider on a commuter-packed I-95 and stands in the middle of the fast lane. In a nerve-jarring game of chicken, he points to the driver of an oncoming red Oldsmobile, motioning him to pull over.

The motorist, already slowing down, brakes to a stop on the divider-shoulder. He has just become arrest number one of the College Park state police barrack's special radar unit, out to enforce the 55-mile-per-hour speed limit by cracking down on violators.

A half-mile down the road, nestled in the lee of a grassy hill and a fence, sits an innocuous unmarked blue Plymouth, manned by trooper Chris Iden and his radar apparatus. He radios to Churchill the clocked speed: 75.

Iden and Churchill were part of a three-car special radar detail, on duty yesterday morning as part of Gov. Harry Hughes' $200,000 program to save energy by enforcing the 55-mile limit. The money, which state police spokesmen estimate should cover 25 weeks of extra radar details, he is being used by police barracks across the state to beef up their usual radal operations.

It is still early in the program, which began at midnight Tuesday, to determine what the long-range effect will be. But State Police Lt. Tom Moore said last night that tallies for Tuesday showed 586 speeding arrests statewide, up from 583 arrests on an average day in May of last year. "Our goal is to slow it down, not to write more tickets," he said of the slight increase.

Moore said that roughly a fifth of the speeding citations were written in the Washington area and a reporter's trip to the College Park radar unit showed the effects of the extra patrol: 18 of 57 summons for speeding issued Tuesday were written by an overtime unit.

Yesterday, the unit stationed itself on the southbound side of eight-lane I-95, just after the Washington-bound commuter passes Rocky Gorge Dam on the Patuxent River. Trooper Iden tucked his unmarked car in a spot the motorist is likely to overlook until it is too late.

On the trooper's dashboard sits a clock-radio-like gizmo, the Decatur 715. Instead of the time, the instrument silently flashes the speeds of passing cars. Iden said he set the alarm number at 66, but cautioned the speeding cutoff varies from day to day according to traffic conditions.

Two thirds of the cars that whipped past Iden were exceeding the 55-mile limit, but just a relative handful was going fast enough to trigger the alarm's beeper. Setting the instrument lower, Iden said, would net far too many motorists, overburdening the troopers and causing a traffic jam.

Not everyone who set off the penetrating alarm ended up paying the full penalty, however. One Virginia woman was let off with a warning. A young woman with a college decal on her car was cited for fewer than the maximum number of points after pleading that it was the first time she had been stopped for speeding.

"We sometimes do that when they're agreeable," explained Trooper Dan Austin, adding that offenders who insist the radar is wrong are less likely to get a break.

Other speeders tried to outsmart the system. Some, noticing Iden's unmarked car, gradually slowed down and cut from the fast lane, four lanes away to the slowest, in the hope that the troopers waiting to flag down violators wouldn't notice or dare to cross four lanes of traffic to pull them over.

Sometimes, Iden says, the speeder wins. Indeed, a small truck maneuvered its way through thick traffic to elude the troopers' call.

Among those caugh, the reactions varied. Agnes Warfield, who was clocked 67 on her commute from Columbia to Washington, wore a pained expression and claimed she wasn't aware of the speeding crackdown as Austin drafted her ticket.

Another motorist was more philosophical. "I think it's a great idea to save energy." he said. "I'm just sorry I got caught."