Loudoun County Sheriff Donald Lacy decided this spring not to seek a second term, but, nonetheless, he has become a major issue in the two-man contest for sheriff of the spacious, rapidly growing county.

Democratic candidate John R. Isom, 41, a retired, 20-year veteran of the Fairfax County police force and resident of Sterling, puts it bluntly. His platform is "to provide an example of personal integrity and honesty that we didn't have under the last administration," he said. "I want to restore public faith and support for the department that was lost under Lacy."

Republican candidate Leonard W. McDonald Jr., 35, a captain in the Loudoun sheriff's department with 12 years of service, said that's not the most important issue.

"My opponent may attempt to make a connection between the sheriff and myself . . . but it should be noted that I have been here longer than the current sheriff and have served under two sheriffs. . . . We are two separate individuals. I have different positions and philosophies than the two other people I served under."

So the lines have been drawn for the Nov. 8 election: Isom doing his best to attack his opponent's former boss and thereby his opponent; McDonald doing his best to disassociate himself from the tarnished personal reputation of the man he served and often substituted for during the past four years.

Lacy took office in 1979, the county's first Republican sheriff, ousting a longtime Democrat and highly touted as the man who would transform the "country" sheriff's department into a professional law-enforcement agency.

And although Lacy is credited with increasing his department from 68 to more than 102 officers and quickening response time in the county, he has spent much of his tenure defending himself against accusations of mismanagement and personal and financial improprieties.

Last year, a special investigative grand jury issued a strongly worded eight-page report, citing Lacy for alleged misconduct, misuse of county funds, "making a fool of himself" by drinking in public, intimidating members of his department, helping to cover up improper information in a search warrant and agreeing to drop criminal charges at the request of his friends.

The jury also probed "numerous charges of sexual misbehavior" but said it doubted any of the charges could be proven in court. Finally, the jury urged Lacy to resign but did not recommend that any criminal charges be filed against him. A petition drive to remove Lacy from office failed.

Lacy denied all the allegations, branding efforts to oust him a "Latin American-style coup d'e'tat." After carrying on what some county politicians called an "absentee administration" for the past 18 months, Lacy announced this spring that he would not run for a second term.

Now Isom and McDonald are on the Loudoun campaign trail, walking door to door and eating fried chicken at church suppers, vying for Lacy's $35,000-a-year job as the county's chief law enforcement officer.

Isom, who retired recently as a captain and night commander of the Fairfax County force, has been a resident of Sterling for the past four years.

The son of a Tennessee farmer, Isom said that even though he is a newcomer to Loudoun, and therefore not a part of the "good-ol' boy network" that he says long has run the county, "I'm saying to them that, 'Hey, I chose to live here. I'm here by choice, not because I was accidentally born here. I've lived all over Virginia, and I think this is the most appealing place I've lived.' "

If elected, Isom said he would seek to raise the $14,500 base pay of deputies to attract "higher quality deputies who would stay longer." He also vowed to establish uniform standards of performance and promotion, recruit blacks and other minorities, institute a police cadet program and an auxiliary deputy program and expand neighborhood watch programs.

McDonald said that "after 12 years on the force , I decided to give it a shot. I thought it over very carefully . . . and felt they needed someone from the county and from the department who could lead by example and had progressive ideas and a professional attitude toward law enforcement."

McDonald, the son of a farmhand, was born in the rural, western end of the county and now lives in Leesburg. He said what he offers Loudoun residents is an understanding of the way the county works, rooted in his own lifelong residency.

McDonald said he also favors increasing pay and standards for deputies. Also in his plans are the creation of a citizen's advisory committee and a resident deputy program, under which residents of the same neighborhoods as deputies can go to the officers with their concerns and fears.

McDonald also places neighborhood watch programs, which he helped implement in the county, high on his list.

"I know the department, its strengths and its weaknesses," McDonald said.

"I have 20 years of police experience, 13 of them at a command level," Isom said. "I know how to run a department."