Thomas Eugene Spinks, one of three Maryland men indicted in the bombing of 10 abortion clinics and related facilities in Maryland, Virginia, Delaware and the District, pleaded guilty today to one count each of conspiracy and malicious destruction in the blasts.

Spinks, a 37-year old roofer and chimney sweep from Laurel, entered the plea before federal Judge Alexander Harvey II. Currently in jail without bond, he will be sentenced in about six weeks. He could receive a maximum penalty of 15 years in prison and $20,000 in fines.

Spinks' plea leaves the other two defendants, Michael Donald Bray, 32, of Bowie, and Kenneth William Shields, 34, of Laurel, facing trials soon with the possibility that Spinks will testify against them.

The plea, considered crucial by prosecutors in their conspiracy case against Bray and Shields, came only hours after Assistant U.S. Attorney Robert B. Green announced in court that the government has evidence that at least seven others were involved as "coconspirators" in the bombings in 1984 and early 1985.

Green did not name the additional suspects in court and refused to discuss them with reporters outside court or to say whether more indictments are expected.

Separate trials for Bray and Shields are scheduled to begin May 13 and June 3, respectively.

They are charged with conspiracy to damage property and possess illegal destructive devices as well as with actual possession of pipe bomb ingredients and other destructive materials. Both have pleaded not guilty. Spinks was originally charged with detonating explosives at five of the blast sites.

The charges stemmed from a wave of nighttime bombings and arsons that ripped through 10 abortion clinics and counseling offices, most of them in the Washington suburbs of Maryland. There was extensive damage to buildings, but no injuries were reported.

Spinks, viewed by prosecutors as the principal defendant in the case, has been held without bond since his arrest last January. Bray, a housepainter, and Shields, controller of a Warrenton, Va., firm, are free on bond.

All three have been described by law enforcement officials as fervent religious opponents of abortion. Bray is a lay copastor of the Reformation Lutheran Church in Bowie, a splinter group that broke from the mainstream Grace Lutheran Church in Bowie because it felt Grace Lutheran was "not strong enough" on abortion and other moral issues, according to Michael G. Colvin, fellow copastor with Bray. Colvin has repeatedly stated that both he and Bray are opposed to the use of violence in closing down abortion clinics.

Bray has said in an interview that, while he has chosen not to destroy property as a tactic against abortion, "I cannot condemn those who have [chosen otherwise]."

He has also said he and Spinks know each other through church and participation in antiabortion picket lines. Agents say Shields also has acknowledged knowing Spinks and giving him technical information about explosive devices.

Agents of the U.S. Bureau of Alcohol, Tobacco and Firearms and other officers said they linked the 10 bombings through similar ingredients found in bomb fragments at the blast sites. They said they traced purchases of chemicals and other materials to Shields and Spinks and surveillance of two abortion clinics to Bray. One ATF agent testified at a bond hearing that officers found strands of hair on a piece of tape attached to a bomb fragment at one site that matched Bray's in more than 25 characteristics.