HELENA, Mont. - Investigators found a partially assembled pipe bomb, chemicals and meticulous notes on making explosives in the mountain cabin of the former Berkeley math professor suspected of being the Unabomber, federal officials said yesterday.

Theodore John Kaczynski, 53, was charged yesterday with possessing the bomb components and was held without bail. Appearing before a judge, Kaczynski, bearded and thin, said he was mentally competent and couldn't afford his own lawyer.

The charge made no mention of the Unabomber's string of bombing attacks, which killed three people and injured 23 in 18 years. Federal officials said the charge was designed to hold Kaczynski while agents build a case.

The FBI again searched Kaczynski's hand-built, 10-foot by 12-foot cabin Thursday. Federal officials said the search could last several days.

The cabin has no electricity or no running water, which would appear to match the Unabomber's aversion to modern society and technology.

FBI agents had been staking out Kaczynski's cabin near the Continental Divide for several weeks, ever since his own mother and brother in the Chicago area notified authorities that they had stumbled across some of his old writings and found them similar to the Unabomber's anarchist manifestos.

Kaczynski was taken into custody by federal agents Wednesday so they could search his cabin in the wilderness 50 miles northwest of Helena.

FBI and Bureau of Alcohol, Tobacco and Firearms agents found a partially completed pipe bomb in the loft at Kaczynski's cabin, according to an affidavit by FBI agent Donald J. Sachtleben.

Ten three-ring binders were recovered filled with ''page after page of meticulous writings and sketches which I recognize to be diagrams of explosive devices,'' Sachtleben said.

In addition, FBI and ATF agents found galvanized metal, copper and plastic pipes, four of them with copper plates sealing one end, ''one of the first steps in the construction of a pipe bomb,'' Sachtleben said.

A federal grand jury is scheduled to convene April 17 in Great Falls and will decide whether to hand down an indictment in the case, a federal law enforcement official said on condition of anonymity.