Dr. Pedro Servano always believed that his journey from his native Philippines to the life of a community doctor in Pennsylvania would lead to American citizenship.

But the doctor, who has tended to patients here in the Susquehanna Valley for more than a decade, is instead battling a deportation order along with his wife.

The Servanos are among a growing group of legal immigrants who reach for the prize and permanence of citizenship, only to run afoul of highly technical immigration statutes that carry the severe penalty of expulsion from the country. For the Servanos, the problem has been a legal hitch involving their marital status when they came from the Philippines some 25 years ago.

Largely overlooked in the charged debate over illegal immigration, many of these are long-term legal immigrants in the United States who were confident of success when they applied for naturalization, and would have continued to live here legally had they not sought to become citizens.

''It's no wonder there are so many illegal immigrants,'' said Brad Darnell, an electrical engineer from Canada living in California who applied for citizenship but is also now fighting deportation. ''The legal method is so intolerant and confusing.''

A legal immigrant since 1991, Mr. Darnell is married to an American and has two American-born sons. But after he presented his naturalization application last year, Mr. Darnell discovered that a 10-year-old conviction for domestic violence involving a former girlfriend, even though it had been reduced to a misdemeanor and erased from his public record, made him ineligible to become a citizen -- or even to continue living in the United States.

Since 1996, when an immigration law overhaul first brought intensified scrutiny of citizenship applications, at least 85,000 naturalizations have been turned down each year.

The record year was 2000, when 399,670 applications were denied, one-third of those presented, according to an analysis by the Migration Policy Institute, a nonpartisan research organization. More recent denial rates remain high, but have fallen from the peak because more immigrants have prepared with civics classes and immigrant advocates before applying to become citizens, researchers said.

In three recent cases in Florida, aspiring citizens thought their green cards entitled them to vote or register to vote before they were sworn in as Americans. When the immigrants reported their elections activities on their applications, not only were their naturalizations rejected, but they were also ordered to leave the country, according to their lawyer, Jeffrey Brauwerman.

In a current Florida case, a British-born businessman saw his naturalization derailed and was detained for deportation because he forgot to update his home address with the immigration agency, Mr. Brauwerman said. He was charged with ignoring a notice in which immigration examiners mistakenly accused him of a felony he had never committed.

In a case that drew Congressional attention this year in Illinois, Marin Turcinovic, an immigrant from Croatia, was twice denied citizenship because he did not show up at the immigration office to be fingerprinted. As his lawyer explained to no avail, Mr. Turcinovic was a quadriplegic, dependent on a ventilator and unable to leave his home.

Mr. Turcinovic died in April 2004 without becoming a citizen, creating an immigration crisis for his French widow, Corina, who had taken care of him. In January Representative Daniel Lipinski, Democrat of Illinois, presented a bill that halted her deportation.

Immigration officials say denials have increased in the last decade because naturalization applications are increasing. They note that approvals are rising as well. In 1996 naturalizations soared for the first time to more than one million, and they remained above 450,000 each year through 2007.

''Whenever we see a period when large numbers decide to apply, there tend to be larger numbers of people who are not ready or might not meet the requirements,'' said Chris Rhatigan, a spokeswoman for Citizenship and Immigration Services.

Officials said the majority of denials went to applicants who failed a required civics and English language test or fell short of residency requirements. Those immigrants generally can try again.

But as the case of the Servano family illustrates, some denials come as a shock to both the applicants and the communities they call home.

Dr. Servano's mother, five siblings and eight of his wife's siblings became naturalized citizens, including one brother and two brothers-in-law who made careers in the Navy. His four children are Americans by virtue of being born here. He has been a legal immigrant in the United States for 25 years.

Following an outcry from neighbors, patients and local officials, Department of Homeland Security officials in December temporarily suspended the Servanos' deportation. The Servanos and their supporters, including Senator Arlen Specter, Republican of Pennsylvania, are using the unusual reprieve to pursue new legal efforts to resolve the couple's case.

Dr. Servano and his wife, Salvacion, lived for years in the United States with no inkling they might have violated the law. They met in the Philippines when she was a nurse and he was a young traveling doctor. Her strict father insisted she marry, they said, but his family wanted him to wait.

In the early 1980s, their mothers came separately to the United States as legal immigrants and petitioned for residence visas, known as green cards, for Pedro and Salvacion under the category of unmarried children. But between the time the visas were requested and when they were issued in 1985, Pedro and Salvacion, hoping to escape conflicting parental demands, secretly married in the Philippines.

Unaware that their marriage could have violated the terms of their green cards, the Servanos settled in the United States. He completed a second medical residency here and began to practice in blue-collar towns where he made house calls and was known for attention to everyday ills. He and Salvacion married in New Jersey in 1987. They renewed their green cards punctually.

''My goal is to be fully functional and integrated into the society,'' Dr. Servano said. They presented their 1991 naturalization applications without seeking a lawyer.