The Rockville home of the chief pro-Israel lobbyist in Washington was heavily damaged yesterday morning by a powerful bomb that shattered windows over a five-block area but "miraculously" spared the lives of the sleeping family members, Montgomery County police reported.

As of late yesterday, investigators said they had established no motive for the 3:20 a.m. bombing, which caused at least $50,000 damage to the $100,000 home of Morris J. Amitay, executive director of the American Israel Public Affairs Committee (AIPAC).

Whoever touched off the blast - for whatever purposes - was considered "sophisticated" in the use of explosives by both local and federal investigators. They noted that the bomb was apparently triggered from another street by an electrical device connected to the explosives via a 400- foot electrical cord found at the scene.

Amitay, 41. as the chief officer of AIPAC, heads the only domestic group registered to lobby on behalf of pro-Israel legislation on Capitol Hill. Amitay's position immediately prompted speculation by many members of the Jewish community that pro-Palestinian terrorists were behind the bombing. Representatives of some of the major Palestinian groups denied involvement, however.

Police also discounted the possibility that members of the Hanafi Muslim sect. some of whose members were convicted Saturday in connection with the armed takeover of the Washington headquarters of a national Jewish service organization, were involved in the bombing.

No individual or organization called to claim reponsibility for the bombing, according to police. Nor was there any "information" that any other group, such as the Ku Klux Klan or a neo-Nazi organization, was reponsible, they said.

Amitay, who served at one point as top foreign policy advisor to Sen. Abraham Ribicoff (D-Conn.), declined to comment on the bombing yesterday. Police said that Amitay told them that he had not received any tahreats before the bombing.

Amitay, his wife, Sybil. 36, and three children, aged 14, 12 and 9 were asleep at the home at 4712 Sunflower Rd. when the explosion blew in the wall below the children's bedroom according to police, friends, and neighbors.

The resulting blast punched out a hole ten feet in diameter. The windows of all upstairs rooms were shattered as were sections of the attic and the home's overhanging roof. A yellow drain pipe was twisted in place and resembled crepe paper.

The family beagle puppy, which had reportedly been barking moment s before the explosion was killed by the blast, police said.

Lt. Leonard King of the Montgomery County Fire and Rescue Squad. said the exact nature of the explosive material used had not been determined. He added that investigators also could not state for certain how close to the two-story brick home the bomb had been placed.

"It was the loudest noise I've ever heard, like a supersonic bomb," said neighbor Roy Bryant, whose roof at 4716 Sunflower Drive, next door to the Amitay home, was lifted several inches off its struts.

The bomb was apparently detonated by someone who ran a 400-foot-long hardware-store variety electrical extension cord from the curb of adjacent Bitterroot Drive. The Amitay property is at the corner of Sunflower and Bitterroot.

The electrical cord, in long black and yellow sections, was run between several small trees, past a brown picket fence outside the Amitay kitchen, then around the corner to the basement wall where the explosion occurred, police said.

The ends of the cord found near Bitterroot were spliced, indicating that it had "probably" been attached to a detonating device, known as a "hell box." according to John Rowley, head of the Washington area office of the Federal Bureau of Alcohol. Tobacco and Firearms.

The first neighbor on the scene after the blast was Sheila Sipes, of 4704 Sunflower Road. "I asked Mrs. Amitay if she was all right and she said, 'My house just exploded.' I asked here if she had any gas, thinking that the explosion was caused by a gas leak, and she said, 'I think my dog is dead,'" Sipes related.

"I went around to look at he side of the house and I cut my foot on a piece of shrappel. When I picked it up I smelled powder, gunpowder, cordite powder," she said. Sipes then brought blankets for the Amitay children, who were hudled in the family station wagon parked in the carport, she added.

The neighbor on the other side of the Amitay property. Wada Jean Tranhern. of 15108 Bitterroot, said whe was awakened by the sound of a lamp crashing from her bedroom wall. "I thought. My God, there's been a gas explosion. I walked around the house and all the windows were broken. I heard the fire engines and realized it was at the Amitay's" she said.

One house down the block at 15101 Bitterroot. Mrs. Roland Sener said she was awake with her windows open at the time of the blast, but heard nothing before the explosion. "I was reading the Helen MacInnes spy novel 'Agent in Place'. The explosion was the loudest sound I have ever heard in my life," she said.

Morris Amitay is regarded as the key pro-Israel lobbist and as an extremely effective persuader. One former Senate aide who revuested anonymity said yesterday that Amitay has been known to "shout over the telephone at Senate aides who disagreed with his position. He threatened to call all of the Jewish organizatins in a major industrial state and say that the senator was warfflington Israel' if the senator did not vote for a particualar bill."

Amitay's fervent belief in the preservation of the Jewish state of Israel was attested to by associates interviewed yesterday, and he reportedly had no outside business interests.

As a former State Department official, he served in Italy and South Africa, and speaks Italian, French, Hebrew and Afrikaans.

Amitay has also been a legislative assistant to Rep. Robert W. Kastenmeier (D-Wis.) and Sen. Abraham Ribicoff (D-Conn). He left Ribicoff's staff after four years to take the AIPAC post in December, 1974.

Friends and associates of Amitay, whom they described as "abrasive" and "pasionate" in his lobbying on behalf of Israel. said they believed his home was bombed because of his "highly visible" position as a promoter of pro-Israel legislation.

They noted that Amitay had been identified as a prominent pro-Israel lobbyist in a number of recent articles as well as a book dealing with the "Jewish lobby" in Washington.

In July, 1973, the Israeli air and naval attache here, Col. Yosef Alon, was killed in a hail of bullets outside his home in Bethesda. Montgomery County police never arrested anyone in the case.

The bombing was immediately condemned by local and national Jewish organizations as a "terrorist" act.

"The bomibing comign only a few days after the visit of Israeli Prime Minister Menachim Begin and aimed at a leading American proponent of U.S. American friendship underlines the tension that still exists and the need for achievinga a just and durable peace," said David Goren of the local chapter of the American Jewish Congress.

A spokesman for the Palestine Liberation Organization, the chief Palestinian umbrella organization. "condemned" the bombing yesterday.