When it became clear Monday night that Montgomery County State's Attorney Andrew L. Sonner had been endorsed by a narrow margin By Democratic Party officials, the rejoicing at Sonner's cardtable headquarters was quick and emotional.

"Thank you for your help, than you, thank you," Sonner, 43, told supporters at the Montgomery Democrats' convention, shaking hands with the men and kissing the women. His response was more typical of an election night victory than a pre-primary endorsement.

Sonner, a two-term incumbent, had entered the endorsing convention with his back to the wall. Last week the Democratic Coalition had by a razor-thin edge endorsed Sonner's little known rival, Assistant Montgomery County Attorney Dan Cassidy, for the job as the county's chief prosecuter. The Coalition is a group of Democrats whose membership is open to all registered county Democrats.

Although Sonner has consistently downplayed the importance or even need for endorsing conventions, two losses in as many weeks might have given the appearance that he had lost support within his own party.

"The pressure was fierce," said one political observer, who declined to be named.

Seeking to gather all the convention support they could, and head off Cassidy's momentum, Sonner's forces began a telephone campaign over the weekend to convince delegates to vote for their candidate.

Several people complained, however, that the methods used by the Sonner callers were more rough than necessary, and not in keeping with the soft-as-a-feather image county politicians like to pretend are used exclusively by everyone in the county.

For example, Sel Freedman, a long-time political activist and one-time Sonner supporter, said he received a call at his home on Friday night from a woman who identified herself as the wife of one of Sonner's assistants. "She said she was calling from the State's Attorney's office, and wanted to know how I was going to vote," Freedman said.

When he declined to tell her, the woman persisted, and again pointed out that her husband worked for Sonner. "I was really amazed that she would be saying these things to me, so I asked her where she was calling from, and she said this time that she was calling from her home," said Freedman.

"If I weren't as experienced as I am, I would have been intimidated by her call," he said.

At noon on Monday Maureen Potters, a precinct official, received a call at home "from someone named Jeff who said he was calling from Andy Sonner's office," Potter said.

Potter said the man repeatedly asked her, "Who are you voting for, who are you voting for?" Potter said she repeatedly replied only that, "I'll be there." The man then asked her, "Then you haven't made up your mind, have you?" she said.

Sonner said if such an event had taken place, it was a mistake, But the man may actually have been calling from his campaign committee, and not from the state prosecutor's office, he said.

"I'm an adversary, a trial attorney, and maybe there's some overuse of the adversarial skills," Sonner said Monday night. "I don't think I've ridden roughshod over anyone. The convention was hard fought, that's all."

Sonner has acknowledged in speeches to each of the two Democratic Party groups that he may have "antagonized" fellow Democrats with his opposition to the endorsement conventions be nevertheless entered, and with his partisanship in the post.

"But I am ready to work the ticket after the Sept. 13 primary," he said Monday night.

Dan Cassidy, 30, who is making his first bid for public office, took heart from the close 198 to 186 defeat. "He's been in office for eight years, and I was unknown six months ago. I think that's quite an accomplishment," he said.

Cassidy is campaigning against Sonner on a platform of charges that Sonner himself never prosecutes cases personally, that plea bargaining by defendents is accepted too readily by prosecuters, and that if elected he will set up a critizens advisory committee on what kinds of crime should be prosecuted. "It's time for a change," he said.

Sonner said he has a hand in the prosecution of all cases in his office, and that if he were in court all the time he wouldn't have time to administer. He has said in conferences that plea bargaining is not overused, and that a citizens advisory committee would be too cumbersome to be effective.

There are no Republicans who have announced for the race, according to John Whiksey, chairman of the county Republican Party's candidate recruitment committee. Democrats hold a three-to-one edge in voter registration in the county, according to official figures.ne edge in voter registration in the county, according to official figures.