President Reagan, in a speech that appeared to reflect White House hopes for a summit with Soviet leader Mikhail Gorbachev, yesterday welcomed "indications of change" in the Soviet Union and played down his normally sharp anticommunist rhetoric.

The speech, to a Captive Nations Week gathering that is aimed at publicizing human-rights violations in nations under Soviet domination, came in a week in which the Soviets agreed to a key element in arms control talks: the global elimination of medium-range nuclear weapons. A White House official said later that the president is not retreating from any positions but is trying to avoid being provocative as the two countries approach what is expected to be a fall summit.

"There are indications of change coming from the Soviet Union, and those are welcome," Reagan said yesterday, departing from his text. "But we should not and cannot turn our attention away from those who look toward the day there is improvement in human rights and basic freedoms."

The president's 15-minute speech, delivered to a luncheon audience of nearly 300 at the Ukrainian Catholic National Shrine in Northeast Washington, did attack the Soviets for their suppression of freedoms in countries allied with the Soviet Union.

In the talk, however, Reagan passed over several pointed references to Gorbachev in his text and at one point appeared to link Soviet abuses in other nations to one of Gorbachev's predecessors, Leonid Brezhnev.

"Let us hear that the so-called 'Brezhnev Doctrine' is no longer policy, {that} it is null and void," the president said. "Let the Kremlin announce or renounce the use of force as a means of imposing on any people a form of government they do not choose."

The president recounted the tale of Petro Ruba, a prisoner held in the Soviet gulags, first for making a wooden replica of the Statue of Liberty and then for criticizing the Soviet invasion of Afghanistan. Reagan urged that Ruba be freed, but he omitted addressing that appeal directly to "Mr. Gorbachev" as his prepared text did.

Reagan also dropped a line saying that if Ruba is released "we will know that glasnost {Gorbachev's policy of openness} is not just the 20th century version of a Potemkin village," a reference to an 18th century ploy by Russian Empress Catharine the Great to make the lives of the peasants appear idyllic.

Last year, in the White House observation of Captive Nations Week, Reagan spoke of a "massive military buildup" by the Soviets and had dissident Anatoly Shcharansky as his guest at the White House when he signed a proclamation for the week.

The president appeared upbeat and buoyant throughout an hour-long luncheon with refugee community leaders, most of East European descent. "We joked; his jokes were better than mine," said Lev E. Dobriansky, former U.S. ambassador to the Bahamas and a Ukrainian American who long has championed the "captive nations" cause.

The president used the forum to reiterate, without mentioning the Iran-contra hearings as a cause, that public support for the contras fighting in Nicaragua is growing.

"I predict that the increased awareness of the American people . . . will permit us to continue providing weapons and support to those brave individuals who are struggling for the right to choose freedom and not continue a communist dictatorship in their native Nicaragua," he said.

Administration officials expect that Reagan will ask Congress for $140 million to fund the contras for 18 months after the current budget expires in October, funding that would last into the next administration.

Many in the captive nations group appeared happy with his speech, although several noted Reagan's rhetoric was not as strident as in the past. "Very positive without using very big words," said Laszlo Pasztor of Pittsburgh, chairman of the National Federation of American Hungarians Inc. "No one wants to be a warmonger."