Working from a fingerprint on a piece of tape, tracing explosives to the point of purchase and comparing handwriting samples with those on receipts for the goods, Bureau of Alcohol, Tobacco and Firearms agents used "every available investigative technique" to collect evidence that led to the arrest of three Maryland men Saturday in connection with eight bombings of abortion clinics and facilities of sympathetic groups in the Washington area.

ATF agents left open the possibility of additional arrests in the Washington attacks and continued to keep the house of Michael Donald Bray, 32, of Bowie, one of the men arrested Saturday, under surveillance, according to Bray's wife, Jane.

"It's a continuing investigation," said Phillip C. McGuire, associate director of ATF's office of law enforcement.

ATF Special Agent Michael Bregman, in charge of the Washington operation, said a search of the house of another of the arrested men, Thomas E. Spinks, 37, also of Bowie, uncovered evidence "indicative that they were involved in the manufacture of explosive devices at the residence . . . . The house was a public safety hazard."

Another ATF source said agents also removed "ready-to-go" bombs from Spinks' home at 12405 Salem La. More than 20 carloads of ATF agents and other police officers arrived at the house to execute a search warrant Saturday night, and a squad equipped with bomb disposal devices entered the house while Spinks' wife was being interviewed at her door by a reporter.

According to a court affidavit, a major breakthrough in the case came when a fingerprint on a piece of plaster tape found after the Nov. 3 bombing of the American Civil Liberties Union office on Pennsylvania Avenue SE led federal agents to concentrate their investigation on Spinks.

The affidavit also stated that, in the opinion of a federal documents expert, it was "highly probable" that a name on a receipt for the purchase of chemicals that could be used to make explosives was printed by Spinks.

Friends, clergymen and relatives of the three men charged in the bombings -- Bray, Spinks and Kenneth William Shields, 34, of Laurel -- described them as fervent Christians who met through the close-knit religious community in the Bowie area and who share the antiabortion sentiments of many in that community.

ATF agents, who worked with police and fire officials from six local jurisdictions, said they followed the men Saturday with a surveillance plane flying out of the College Park Airport.

With Saturday's arrests, the ATF believes it has now solved a total of 20 of 31 attacks on abortion clinics and related facilities nationwide since 1982. ATF sources said they did not believe the Washington bombings are linked to those elsewhere. "We have absolutely no evidence of a nationwide conspiracy," ATF Director Stephen Higgins said at a news conference Saturday night.

Bail hearings for the three men are scheduled Tuesday.

Although the ATF last month warned abortion clinics to be alert for the possibility of violence during the presidential inauguration and the 12th anniversary tomorrow of the Supreme Court decision legalizing abortion, ATF officials said yesterday that the timing of the arrests was accidental.

"Our main concern was putting a stop to the bombings before someone got injured or killed," added a top ATF official involved in the investigation. "The fact that as it turned out it happened this weekend . . . . It tickles us to death to do it . . . but it was not planned this way."

The arrests came as antiabortion protesters began a weekend of picketing and demonstrations that will culminate in a massive March for Life tomorrow, and as the National Organization for Women was holding overnight vigils at 27 abortion clinics across the country to demonstrate that "prochoice" activists have not been intimidated by the attacks. At least one local clinic received a bomb threat last night.

Several people who knew the three men arrested yesterday expressed shock at the arrests, and pastors of several churches where the men had worshiped asked their congregations to pray for them.

"My impression of all three is that they are hard-working family men, Christian-oriented, and I'm utterly devastated at the fact that they'd even be charged with this," said William Schuhl, president of the Bowie-Crofton Right-to-Life chapter, to which Bray belongs, and a member of Cornerstone Assembly of God, Shields' church.

"I and our congregation were very shocked and grieved over this whole situation, that three men that we knew . . . had been arrrested for this," said the Rev. Kenneth Burtram, the pastor of Cornerstone, where Spinks worshiped until last year. "As a congregation, we believe that abortion is wrong, but we believe that the way to handle the issue is through the governmental means at our disposal."

Bray, a member of the Pro-Life Nonviolent Action Project, also had been arrested Nov. 17 in the project's sit-in at a Wheaton abortion clinic. The three men are charged in the bombing of the clinic, along with that of a family planning office in Rockville, two days later.

All three men are married, with children.

Michael Colvin, copastor with Bray -- a lay minister -- of the Reformatory Lutheran Church, said that Bray, who worked part-time as a painter, and Spinks, a self-employed roofer, became friendly working together on a construction project. Bray said in an interview Saturday shortly before his arrest that he and Spinks did not know each other well but had once marched together in An abortion protest and had attended the same church.

Spinks and Shields have been friends for years, and they once worshiped at the same church in Laurel, friends said.

Neighbors described Spinks as a fervent Christian who often approached residents of the upper-middle-class neighborhood to ask if they had accepted Jesus as their savior. Otherwise, neighbors said,, Spinks and his wife Beth did not mingle with residents, and their three sons, who attend a private Christian school in Bowie, did not play with others in the neighborhood.

A top ATF official involved in the investigation said yesterday that the bombs used in the eight incidents were sophisticated devices that were of different designs but contained similar explosive materials. The official said munitions dealers to whom they traced the materials provided them with details for a composite drawing of one of the men.