Only now, 51 years after he fled his Texas childhood and proved he could work his way through high school, college and medical school, that he could set up his first black medical practice in Annapolis and later that he could represent that city in the state legislature, is Aris T. Allen willing to talk about his past.

"When I was 5 years old my mother sent me off to my father in San Antonio," he begins. "It was an unhappy situation. My father and I had disagreements. So I walked out at 16, I never saw my father again."

That terse summary of years of poverty, racial discrimination and loneliness is part of the public catharsis of Allen, the Republican candidate for lieutenant governor of Maryland and the first black to run on a major statewide ticket.

Last year, at the age of 66, Allen said he decided to tell his saga publicly for the first time to stem the pessimism of countless young men and women - white and black - who feel as if their lives are over before they are adults. "It's not a past I'm proud of and it's depressing to talk about it but I suppose we can't all be elites."

In this year's political campaign, filled with talk of tax reductiongrowth, management and fiscal prudence, Allen has reminded Marylanders of other issues. Poverty, unemployment, child care, health care and welfare are mentioned regularly when Allen explains why he, a black Republican is seeking office.

"When I was young I was a Democrat. The only opportunity I found was with the federal government, the liberal administrations under Franklin D. Roosevelt. When I moved to Annapolis I discovered that locally, the Republicans cared more," he said.

Opportunity came first in Chicago, the city to which Allen ran after leaving his father. But the story begins in a small Texas town near a railroad station. "One day, when I was 5, my mother said I would have the opportunity to ride on one of those trains. She knew I liked them," Allen remembers.

The ride was a one-way trip in a segregated baggage compartment to San Antonio, where he was sent to live with his father. The youngster first saw his father polishing brass at a hotel, a sight that led Allen to vow to make more of his life than his father had.

Years of arguments followed; Allen will nto volunteer more. Finally, it was Allen's peers who forced him to leave home. "I was literally laughted out of the classroom at the age of 15," he remembers. "I was wearing a pair of my father's shoes because mine had not bottoms. My pants were too short and the children laughed so hard that I left and didn't go back to school for 10 years."

Allen's wife Faye, who is his partner in their Annapolis family clinic, believes her husband's determination stems from those early years of rejection. "He never had a close relationship with anyone. It was painful that no one cared enough to be close to him. It was hard for him because his father felt he was a burden."

In Chicago, Allen worked as a blue print draftsman, auto mechanic, porter and drugstore clerk for 10 years until he passed a civil service test. With an assured full-time job. Allen went back to high school and moved to the District of Columbia.

For nine years he held down eight-hour federal jobs as an elevator operator and later as a guard while he finished high school at Dunbar, college at Howard University and medical school at Howard.

"I suppose the way I grew up has given me a degree of compassion, pride. But I would never, never recommend it for anyone else. You endure, some would say, with strength. I would say it is callousness, a thick skin which is hard to shed," Allen said.

Allen joined the military and the federal government helped out once more, giving him grants to complete his medical education and an alternative to active duty. "World War II was over and the military didn't need doctor. "They said I could go instead into a civilian area where physicians were needed. Annapolis was on their light so I went there to practice in 1945," he said.

He was the first black doctor at the state capital. When Faye Allen became a physician two years later, she joined her husband in the family practice they still have today. In the early '50s, though, their clientele and their lives were quite different.

"Oh, Annapolis was segregated," Allen says. "The very hospital where I'm chief of staff today I couldn't work in then."

The hospital is Anne Arundel General and years ago only county medical society members could practice there. The society would not admit Allen. "When the new young men came to town they finally recommended me as a society member. I went to work at the hospital to find the wards were segregated. Racial discrimination, I would say, worked against me in many ways."

Many of those young physician colleagues of Allen were Republican and he switched party affiliation. A Republican governor appointed him to sit on the local school board and Republicans have since encouraged him to run for the legislature and for lieutenant governor. He has never independently sought office.

Yet Allen has been an anomaly among Maryland's black politicians since he first won election to the House of Delegates in 1966. His Annapolis constituency has never been more than 20 percent black and as a physician he worked as hard to liberalize abortion laws as he did to pass civil rights legislation.

"All you have to do is look at me and know how I stand on any issue of discrimination," Allen says. But one of his black caucus colleagues says, "He was never in the mainstream of black politics."

Besides, Allen is a Republican. "You could say I integrated the Black Caucus," he says. "I think I was the first and the last Republican member it's had."

Since Allen has never been a part of the political hub of state black politics, the Baltimore Democratic group, his candidacy as running rate of J. Blenn. Beall Jr. drew curious reactions among blacks. Nelson R. Stewart, a former Baltimore City state's attorney and a Democrat, contacted Allen last summer to discover, he says, whether Allen was a token for the ticket.

"I wanted to see what he had to say," Stewart said recently. "See if he was a black politician. I was surprised. I liked him. I told him I'd work for him and I've been working ever since."

The Allens practice family medicine, often working 14 hours a day. Routinely, Allen promotes this experience as his greater asset for political office.

"In my 33 years of general practice I have worked with many people, I've had to know them intimately. I know what it means to be on welfare. I know how deparessed they are by it. They want to work," Allen says.

Allen has sought out state welfare rights groups and the people who live in public housing to win their approval and has had some success. He is, as one prominent black Democratic leader phrased it, a fine test to see if blacks will vote for their race and across party lines.