The Reagan administration is discussing a deal that could result in the dropping of drug trafficking charges against Panamanian strongman Manuel Antonio Noriega in exchange for his agreement to relinquish power, a White House spokesman said Thursday.

"We're still talking" about such a deal, said chief presidential spokesman Marlin Fitzwater. "What this amounts to is a plea bargain." However, the spokesman said no direct negotiations have taken place with Noriega on the matter.Pressed at a briefing later to spell out the legal and other ramifications of such a deal in this country, Fitzwater said, "I offer no definition of plea bargaining.

"I'm not going to speculate on possibilities that we don't know are going to happen," he said. Fitzwater did say, however, that President Reagan has not talked to Noriega.

"The president obviously has directed the negotiations that have gone on there, but I won't go further," the spokesman said. "Negotiations are continuing, with no agreements reached."

Earlier, White House chief of staff Howard Baker, without actually confirming an offer, told CBS-TV that if such an arrangement got Noriega out of power, "that would be the most fruitful and productive plea bargain that we have seen in a long time."

Reports of an offer brought sharp criticism Thursday from several senators and Panama's anti-Noriega ambassador to the United States.

Administration sources, speaking on condition of anonymity, said Wednesday that Florida drug-trafficking indictments against the de facto Panamanian ruler would be dropped if he stepped down and left the country for a year. The sources said the Justice Department objected to the offer, which was approved at a White House meeting.

Sen. John Kerry, D-Mass., said if descriptions of the offer were accurate, it would appear to be a victory for Noriega, allowing his loyalists to retain control while he spent "a year's vacation on the Riviera."

"If I were a cop in Boston or Miami or somewhere, I'd sit there and say this administration has sent a signal that crime does pay," Kerry said on the CBS show.

Sen. Alphonse D'Amato, R-N.Y., said, "I think it'd be a terrible mistake to take the word of a drug-dealing killer dictator that he's going to get out and allow free elections sometime next year, and he'd be allowed to stay in until August. And the only thing you're going to have is a transference of power to his cronies.

"For us to be saying that we can trust this man to keep his word is naive," D'Amato said. "We can only consider dropping the indictment after Noriega leaves Panama with his henchmen and with the proviso that President del Valle take over and provide for free elections."

Ambassador Juan Sosa, appearing on the CBS program, said Noriega opponents cannot accept the dropping of charges without any arrangements made for next year's election, the restructuring of the defense forces Noriega controls or the setting up of a government of reconciliation.

Sosa also said the obvious differences among U.S. officials on how to handle Noriega have only helped the leader.

He said if Noriega is to leave, he should leave now and not wait until August, which reportedly would be part of the arrangement between U.S. officials and Noriega.

The reported offer is the latest in a series of administration efforts since February.