The people of Severna Park, a quiet residential community on the Severn River about five miles north of Annapolis, knew all along that Benfield Road was being widened and curbed - the promised reward for enduring months and years of potholes and construction.

But when the painting crews came through and put their lines on the new blacktop, their stripes marked four lanes of traffic with no parking instead of the two driving and two parking lanes the residents expected.

"My reaction was one of shock, of utter disbelief," said Florence Blanck, a 19-year resident. "I was so sure it was just another of the many mistakes on this project that at first I didn't do anything. Then it dawned on me that this was no mistake, it was their intent."

Next door, John and Sylvia Johnston were preparing to move into the split-level house they had just purchased.

"What a way to move in," Sylvia Johnston said. When she began circulating a petition, her new neighbors were only too willing to sign.

At the other end of the rebuilt stretch, Bob Cancilliere proclaimed his concern with a sign atop his Severna Park Inn. "Drive slower on Benfield. I'm walking home."

Cancilliere, who really does walk sometimes to his nearby home, concedes that the old, narrow road was dangerous. "But," he says, shaking his head, "I'm afraid we might have spent $2 million redesigning a hazard."

Many Servern Park residents have petitioned Anne Arundel County officials to reconsider the four-lane configuration of Benfield Road. In response to the complaints, the county opened part of Benfield to off-peak parking.

And, last week County Executive Robert A. Pascal, saying that he didn't mean to be "a stiff-necked bureaucrat," agreed to have the road go back to two driving lanes for a 45-day trial period beginning June 1.

But Pascal, himself a Serverna Park resident, agrees with his traffic advisors that a two-lane highway is dangerous.

Public Works Director George Neimeyer, in a report to Pascal, said the two-lane configuration may add to congestion and lead to accidents as moving cars try to weave from the parking lanes into the middle lanes.

George Frangos, the county traffic engineer, also argues that there is too much traffic for a two-lane road and says Benfield eventually will be four-lane its whole length. He predicts that by 1981 it will be carrying 21,000 cars a day - a figure his predecessor projected as the 1990 volume.

The residents claim the four-laning would lower property values, invite speeding and be especially hazardous in summer when youngsters cross the road to the docks and beaches along the Severn River. They also say that the 35-mile-an-hour signs are being ignored, that it's almost impossible to back out of driveways and that the drainage grates make the road unsafe for bicycling.

They say they don't want the road torn up - only the lanes and parking regulations changed. "The whole problem could be solved with $100 worth of paint," one man said.

Benfield Road is a victim of severna Park's desirability as a place to live for people working in Washington, Baltimore, Annapolis and Columbia, Frangos said. "I can't criticize them for it, but there are just too many people using the road."

Except for the new section, Benfield is two lanes wide with emergency shoulders, for most of its length. Its location along the Severn makes it the only practical outlet for a whole cornucopia of leafy subdivisions - with names like Point Field Landing, Chartwell, Chartwood and Fairwinds.

A new subdivision, Shipley's Choice, will add 1,100 new homes near Rte. 3 at the western end of the road.

At the other end, beyond Benfield's only commercial cluster, the four-lane segment runs into Evergreen Road, a tree-lined, narrow road giving access to the original village of Severna Park and Clif Dawson's, a rambling country store where you can buy everything from amaretto to zweiback.

In this small-town setting, the residents say, the highspeed highway is unwelcome and out of character.

"It's our first house, so we can't afford to move," said Johnston, a counselor at Severna Park High School nearby. "But we're beginning to wonder: Did we buy a turkey? Already we're thinking of replacing the front window with a fireplace, and living in back to avoid the noise."

Johnston, Blanck and others say their main gripe is that they were deceived, that they were led to expect something to match the western end of Benfield, and that was widened and straightened a few years ago.

"If they told me I would have a four-lane highway in front of my house, they would have had a small tornado in their hands," said Mrs. Henry O. Cox, who has lived in the same house for 32 years.

"I know we've been duped," said Frances Stanfield past president of the Severna Forest Community Association.

Robert L. Hinkle, who sold part of his front yard to the county for the road, went door-to-door after the lane markings were put down. He found he wasn't the only one surprised by the four-lane configuration. After his findings were publicized, about 15 persons phoned him to say they had been told the same thing - that it would be only two driving lanes.

"Some of the people who called had moved away, so they had no axe to grind," Hinkle said.

County Executive Pascal says he "gives a lot of credence" to the reports that the police were misled back in 1973, before he took office.

"We're trying to check it out," he said. "I have no patience with any government agency that tells people one thing, then does another. That's where the credibility problem comes from."

Meanwhile, Pascal said, "We have a sensitive problem with the road there. We're moving 13,000 cars a day, and the volume is going up until other roads can be built. We're trying to look at the whole picture, to get some answers."