Amid angry protests that he had embarked on an one-sided inquiry, a freshman senator yesterday set out to establish something that theologians have been debating for 2,000 years: when does human life begin?

Sen. John P. East (R-N.C.), one of the most outspoken new conservatives in Congress, found -- not surprisingly -- that five eminient physicians he invited to testify before a subcommittee he heads agreed with him: life begins at the moment of conception.

None was asked, or volunteered a view on whether abortion is, therefore, murder.

The American Civil Liberties Union said that seven of the eight witnesses were opposed to abortion or had been affiliated with anti-aborton organizations.

On the opening day of what promises to become an emotionally charged debate on the abortion issue, East was also greeted by strongly worded pleas from fellow senators that he invite anti-abortionists to testify, and by scores of demonstrators who added a circus atmosphere to his effort.

Six women, representing a group called the Women's Liberation Zap Action Brigade, were arrested for disrupting the hearing. At two points, the women jumped from their seats in the crowded hearing room holding handpainted signs and shouting: "Stop the hearings," and "A woman's life is a human life."

East, who originally wanted to limit the scope of the hearings to medical and legal testimony, announced he intends to expand late hearings. He pledged they would be "fair, extensive and exhaustive."

At issue is a bill introduced by East's mentor, Sen. Jesse A. Helms (R-N.C.), that would allow states to outlaw abortion. The bill, an attempt to make abortion illegal without a constitutional amendment, proposes that "human life shall be deemed to exist from conception." If it passes, abortion would be the taking of human life, and thus a crime.

Various legal scholars argue such legislation would be unconstitutional under a 1973 Supreme Court ruling in which the court said, "The word person as used in the 14th Amendment does not include the unborn."

The word "abortion," however, was hardly mentioned yesterday. Instead, the hearings before the Senate subcommittee on separatin of power turned into an extended biology lesson as more than 80 reporters and several hundred spectators looked on. Scroes more spectators lined the hallways trying to get into the packed hearing room.

The doctors called to testify were slightly amused by the spectacle and the central question poised by East. "There is nothing new in what we're telling you," said Dr. Jerome LeJeune, a world renowned geneticist and professor at the Medical College of Paris. "There are no revelations before you. This is taught in every school. We ar telling you what we tell evey student."

"This is the first time in 15 years anyone has dared interrupt me speaking," said Dr. Hymie Gordon, chairman of the Department of Medical Genetics at Mayo Clinic in Rochester, Minn. "And it is the first time I ever had to argue the unarguable . . . life begins at conception."

Dr. Micheline Matthews-Roth, a Harvard Medical School researcher, drove the point home, reading from an almost endless series of textbooks that all came to the same conclusion. "The beginning of a human life from a biological point of view is at the time of conception," added Dr. Watson A. Bowes Jr. of the University of Colorado.

The only hint of skepticism came from Dr. McCarthy DeMere, a colorful lawyer and physician from Memphis who has worked with an American Bar Association committee on the same subject. As a physician, DeMere said he had no trouble with East's definition of when life begins. "As a lawyer I have problems with everything."

"You've opened a can of worms and as long as you have done it you have to deal with it," he said.

The politicians appreciated this. "I know of no more delicate issue," said Sen. Bob Dole (R-Kan.). "There is no middle ground."

Sen. Orrin Hatch (R-Utah), who as chairman of Senate Judiciary's Constitution subcomittee had originally intended to cochair the hearings, said he isn't entirely sure the Helms bill is constitutional. The abortion issue, he added, is one of the most controversial Congress will deal with this session and "both sides should be heard."

Hatch, a leading conservative, withdrew from sponsoring the hearings when he became concerned this would not be done. Although he denied any rift with East yesterday, the Utah Republican stayed at the hearings only briefly.

A coalitin of groups favoring abortion has mounted an extensive lobbying effort in recent days, complaining that the East hearings are one-sided and unfair. Twenty-one groups, ranging from the American Jewish Congress to the National Abortion Federation, released separate press statements criticizing the bill and the hearings yesterday.

And Sen. Max Baucus (D-Mont.), the ranking Democrat on the subcommittee, released a letter to East saying he was extremely disturbed that Democrats had not been allowed to call any minority witnesses, and that the minority counsel been denied the right to question witnesses.

The Planned Parenthood Federation, the ACLU, the National Abortion Rights League, and several other organizations said they had been rebuffed by the subcommittee when they asked to testify.