President Reagan, in a twilight assessment, says Mikhail S. Gorbachev has never shown any reason to be mistrusted and in fact is steering the Kremlin away from its old goal of "a one-world communist state."

In what was probably his final White House news conference, Reagan said "trust but verify" remains his byword in dealing with the Russians, but he offered an optimstic assessment of how U.S.-Soviet relations stand at the end of his eight-year tenure in office."The path remains open and the pace of peace continues," he said.

For half an hour, Reagan fielded questions Thursday night in an East Room decorated with Christmas trees hung with silver tinsel. He said it was the Russians - not he - who have changed, but his old anti-communist fire was dampened.

On a pressing domestic issue, Reagan said he would be "deeply disappointed" if President-elect Bush, after assuming office next month, raised taxes to help cut the deficit, which grew to $155 billion this year.

But he quickly added, "I don't think it's going to happen."

The chief executive also told reporters the United States ultimately will have to negotiate with Iran to win release of American hostages in Lebanon. "We would be ready to talk with them," he said of the Iranians.

In addition, he said PLO chairman Yasser Arafat did not go far enough in saying his organization accepts the existence of Israel as a state and condemns terrorism in all forms.

"He has left openings for himself where he can deny that he meant this or meant that, that sounded so clean-cut," Reagan said.

On a day after his fifth and final meeting with Gorbachev, Reagan opened the meeting with reporters by reading a warm statement on the state of superpower relations.

Asked if he believed Gorbachev was trying to make the Soviet Union a less threatening nation, Reagan replied without hesitation, "Yes, I do.

"And I think he recognizes that their massive buildup has been responsible for the great economic crisis that he faces there in the Soviet Union," Reagan said.

Asked point-blank if he trusted Gorbachev, Reagan said, "He hasn't shown me any reason yet that I shouldn't."

However, Reagan said the motto "trust but verify" is one that properly guides Soviet policy, too, and said he did not think Gorbachev "would gamble on believing that he shouldn't protect his own interests, also."

Whether or not the United States and Soviet Union ever become allies, as they were during World War II, Reagan said it was up to the Kremlin.

It could happen, he said, "if it can be definitely established that they no longer are following the expansionist policy that was instituted in the communist revolution that their goal must be a one-world communist state."

The president said "certainly there are indications" the Kremlin is moving that way.

"I do think that there is evidence that they don't like being the pariah, that they might want to join the family of nations and join them with the idea of bringing about or establishing peace." He said he would like to see that happen.

Reagan seemed cool to Gorbachev's call for a cease-fire in Afghanistan, followed by a United Nations-sponsored peacekeeping force and broad-based government. "I'm not sure the U.N. would like that or that the U.N. is prepared to do such a thing," Reagan said.

Moreover, he said it would be unacceptable to stop arming the Afghan rebels unless the Soviet-backed regime ended military operations.

The president said he was "very grateful" for Gorbachev's announcement of a 500,000 cutback in Soviet troop strength but said Moscow still would have superiority in conventional weapons.

Reagan also expressed confidence that Bush believed as he does that Contra forces fighting the government of Nicaragua are freedom fighters and worthy of continued U.S. support.

On the subject of American hostages in Lebanon, Reagan said the United States ultimately would have to negotiate with Iran because the Iranians control the kidnappers.

Concerning that prospect, he said, "There are conditions that have to be met also there. Any time that they are ready to come forward on an open basis, we would be ready to talk to them."

"We cannot enter into negotiating in the sense of what kind of ransom to pay or you're just encouraging more hostage-taking. But there are other channels," he said.

Later, spokesman Marlin Fitzwater elaborated: "We'll be glad to talk, but we've never been able to get them to do that."

Reflecting on the highs and lows of his presidency, Reagan said his "greatest burden" was to have to order troops into "danger . . . to where their lives are threatened, to where their lives are taken." He later expanded that, noting the captivity of hostages in the Middle East.

His greatest joy, he said without hesitation, was the economic recovery - the longest ever during peacetime.