Dr. Hector Zevallos, owner of an abortion clinic, and his wife, Rosalie Jean, were released unharmed on a deserted road near their home early today, eight days after they mysteriously disappeared.

An anti-abortion group called the Army of God claimed responsibility for kidnaping the couple, and investigators are working on the assumption that Zevallos' connection to the clinic was the group's motive.

No suspects have been arrested. There appeared to be few clues in the case beyond a tape recording and a series of letters, written in a semi-Biblical style, which were left for the FBI last Sunday in a deserted restroom in nearby St. Louis. The letters, labeled "Epistles" by their authors, demanded that President Reagan call for an end to abortion.

Zevallos, 53, and his wife, 45, were released beside a motel shortly after 4 a.m. today and told to walk 1 1/2 miles along a wooded path to their home in a country club subdivision here.

Wearing the same clothes they wore when they disappeared, the couple looked worn and distraught, but otherwise in good condition, according to FBI agents and neighbors. One neighbor, Barbara Anderson, quoted Mrs. Zevallos as saying that she remembered nothing about the week she was away.

"She looked like she lost a little weight, like she'd just got out of the hospital or something," said Anderson, who lives next door. "But otherwise she seemed fine."

The couple remained secluded in their split-level, $200,000 home all day, refusing to appear before reporters except for brief picture-taking sessions. "It's good to be home," Zevallos said at one point.

"They're shaken and tired, but they'll pull out of it," said another neighbor who visited them several times during the day.

The release came 36 hours after Glen Young, special agent in charge of the FBI's St. Louis office, issued an appeal for negotiations, saying, "We're running out of time."

FBI spokesmen said no ransom had been paid.

The Zevallos vanished from their home, which borders a golf course, the night of Aug. 12. A bowl of popcorn was left uneaten on the table, the television set was running and lights were burning. Doors were unlocked, and the couples' two Mercedes Benz sedans sat in the garage. There were no signs of a struggle.

An investigation began the next day when Zevallos, a Peruvian who came to the area in the 1950s, didn't appear for work at his Hope Clinic for Women in Granite City, Ill., across the Mississippi River from St. Louis.

The clinic, where hundreds of abortions are performed each year, has frequently been the target of protests by anti-abortion groups. It was damaged Jan. 23 by a fire that police blame on arsonists.

An unsuccessful attempt was made to oust Zevallos from the staff of St. Elizabeth's Hospital, a Catholic institution, when he first opened his abortion clinic behind the hospital in 1974.

Security at the clinic was extremely tight today, and FBI agents spent hours interviewing the Zevallos. The doctor also owns a building that houses an abortion clinic in Shreveport, La.

A trim, athletic man, he is well regarded by his medical colleagues and well liked by his neighbors, who described him as an avid golfer.

"The Zevallos are very quiet, private people. Golf is their daytime pastime, television their nighttime one," said Wanda Hanselman, a neighbor who delivered them a spaghetti dinner tonight. "I don't know what happened or why. It's a bizarre situation."

Little is known about the Army of God. Investigators said they had never heard of the group until Sunday, when the FBI was told in a telephone call to pick up the series of letters, which filled 43 pages, and the tape recording.

One letter, The St. Louis Post-Dispatch reported, said, "Man is evil, man's institutions are evil and are working to deprive man of life, liberty and prosperity in defiance of God's will."