A civil trial opened yesterday in Montgomery County that pits a wealthy Potomac widow against the grandchildren of her late husband, a hard-driving businessman who developed vast land holdings in Rockville and Gaithersburg and once advised President Franklin D. Roosevelt.

On one side is Betty Brown Casey, 66, who inherited $50 million to $100 million from her late husband, Eugene B. Casey, one of the wealthiest landowners and businessmen in Montgomery County.

Contesting Casey's inheritance are 10 of her husband's 11 grandchildren, aged 17 to 32. The grandchildren contend that Betty Casey exerted "undue influence" over a seriously ill Eugene Casey in 1985, prompting him to change his will and leave the bulk of his estate to her and a charitable foundation in his name.

In March 1990, Casey was the target of a car bomb attack that severely damaged her Mercedes but left her with only minor injuries. County and federal investigators have made no arrests in the bombing, saying that Casey and her family have been uncooperative in the probe. Police have not linked the bombing to the family dispute.

Yesterday, attorneys for Casey and the 10 grandchildren detailed divergent versions of the last years of Eugene Casey's life and his decisions to give away a fortune he began to amass in the 1930s.

Albert Brault, representing the 10 grandchildren, said Eugene Casey suffered from dementia shortly before his death in 1986 at age 82. Brault said Betty Brown Casey, the third wife of Eugene Casey, persuaded her husband to make two major changes in his will in 1985 that "disinherited" Casey's six children and 11 grandchildren.

"The grandchildren have been terribly and tragically wronged," Brault told Circuit Court Judge Paul A. McGuckian, who is presiding over the trial, which is expected to last four to six weeks.

"They have lost more than money," Brault said in his opening statement yesterday. "They have lost their family heritage and birthright."

Brault said Eugene Casey, weakened by strokes and illness, changed his will in February 1985 to give his wife half of his estate. Six months later, Brault said, Casey altered his will again, deciding to leave the other half of his fortune -- minus $1 million for each of his six children -- to a foundation controlled by his wife.

Brendan V. Sullivan, attorney for Betty Brown Casey, described Eugene Casey yesterday as a stingy, strong-willed man who considered himself a gentleman farmer. From land holdings in Rockville and Gaithersburg, Casey later built numerous apartment buildings and shopping centers, Sullivan said.

Eugene Casey, Sullivan said, had a reputation as a tightwad. Though his fortune was valued at $213 million in 1983, Sullivan said, Casey told employees to save uncanceled postage stamps on envelopes and, despite pleas from his children, was seldom generous with his money. But Casey was in full control of his mental faculties until his death, Sullivan said.

"This man's mind was working perfectly fine," Sullivan said, pointing to 13 three-ring binders filled with copies of stock transactions and canceled checks signed by Eugene Casey in the mid-1980s. Sullivan said Casey, an adviser on farm policy to Roosevelt, made more than $1 million from stock deals in 1985, the same year he signed 1,600 checks involving $23 million.

Sullivan, who represented Iran-contra figure Oliver L. North, said his client was generous with the Casey children and grandchildren, often giving them money when Eugene Casey refused to do so. "That shows what's inside Betty B. Casey's heart," Sullivan said.

Sullivan said yesterday that Eugene Casey decided to alter his will in 1983 after he concluded that he would transfer control of his vast holdings to his wife rather than to his oldest son. Sullivan said Casey and his son had a "troubled relationship."

According to Sullivan, Casey's children and grandchildren did not challenge Casey's will immediately after the 1985 changes or at his death. They saw nothing wrong with it at the time, he said, and are challenging the will now because of greed. "The silence says it all," Sullivan said.