Anglican Church envoy Terry Waite, arriving here today for talks with Reagan administration officials, said four Americans held in Beirut are "alive and well," although it was not clear whether he had seen or spoken with the hostages during his negotiations for their release.

At a news conference at a Manhattan Episcopal Church center, Waite said he was hopeful about the progress of negotiations with their captors. "I regard it as a good sign that they are talking," he said. "But I am not through."

He was reluctant, however, to supply details about the captors or their discussions. "The situation is highly volatile and very, very dangerous. And I am not being overdramatic," said Waite, the representative of the Rev. Robert Runcie, archbishop of Canterbury. "One false move on my part or one loose word could cost lives."

Waite, 46, was visibly tired after a flight from Athens. His departure Sunday from Beirut had been delayed for two days by fighting in the streets. He is here to brief White House and State Department officials and church leaders on the progress of his talks.

Waite said he was not certain how long he would stay in this country but said he hoped to return to Beirut "in a few days."

The four hostages are Terry Anderson, Associated Press bureau chief; the Rev. Lawrence Jenco, director of Catholic Relief Services, and two officials of the American University of Beirut, David Jacobsen and Thomas Sutherland.

"You can take my word for it, the four hostages are alive and well," Waite said. Asked where he met with them, he replied, "I didn't say I spent any time with the hostages."

Waite said he had no information about two other Americans held hostage, Peter Kilburn, a librarian at the university, and U.S. Embassy official William Buckley.

"It's a mystery," he said. "I wouldn't like to say they are dead until I have proof that this is true. But, genuinely, I don't know."