President Reagan charged today that intelligence services of the Soviet Union and its allies are "hard at work" trying to steal secrets and technology from the United States with "some of the most sophisticated, best orchestrated efforts of theft and espionage in modern history."

In his Saturday radio address, Reagan said that a rash of espionage arrests in recent weeks resulted from more aggressive efforts by the United States to catch spies, and warned that the amount of spying on the United States is on the rise.

Reagan said the administration is responding with "a broad range of reforms and improvements, including reducing the size of the hostile intelligence threat within our borders," and other measures.

Commenting publicly for the first time on a series of arrests of accused spies for the Soviet Union, Israel and China in recent weeks, Reagan said, "We will not hesitate to root out and prosecute the spies of any nation. We'll let the chips fall where they may."

Speaking from his mountaintop ranch near here, Reagan said the "intelligence threat" comes from the Soviet Union and its allies, and did not mention Israel or China, except to say that the spate of recent arrests shows that "many nations spy on the United States."

Last week, civilian Navy counterterrorism analyst Jonathan Jay Pollard was accused of selling U.S. military secrets to Israel, and his wife, Anne Henderson-Pollard, was charged with unauthorized possession of classified documents. In a separate case, Larry Wu-Tai Chin, a retired Central Intelligence Agency employe, was accused of spying for China for more than 30 years. And Ronald William Pelton, a former National Security Agency employe, was accused of spying for the Soviets.

The cases have had intensifying diplomatic ramifications, and the United States has pressed its ally, Israel, to permit questioning of two Israeli officials said to be Pollard's contacts who left the United States after Pollard was arrested.

Pelton, an employe of NSA from 1965 to 1979, is accused of providing the Soviet Union with secret information on U.S. intelligence-gathering activities directed at the Soviet Union. Pelton's lawyer referred to a project called "Ivy Bells" without elaboration during Pelton's bond hearing last week. Whether Pelton actually worked on Ivy Bells or gave the Soviets information about it could not be determined. A senior FBI official refused to comment today on whether Pelton had information about Ivy Bells.

Knowledgeable intelligence sources described Ivy Bells as a highly sensitive signal intelligence project involving the Navy. Signal intelligence includes the monitoring of communications, radar and telemetry, which is data on the performance of missiles and warheads during tests that is radioed to Earth as a test proceeds.

One of the sources said that Pelton, although he was a relatively low-level NSA employe, "caused serious damage in a few areas" of U.S. intelligence-gathering operations. But, the source said, Pelton did not have access to information that would allow the Soviets to break sensitive NSA codes.

The CIA is treating the information allegedly leaked to China by Chin as a serious loss, according to an intelligence official. However, he said, the CIA has not curtailed any operations in the Far East as a result of his exposure as a spy, and the agency does not believe that Chin's information jeopardized any agent networks there.

The intelligence official said that Chin would have known what kind of intelligence information the United States was picking up from China in some instances and could have helped the Chinese locate leaks in their own government.

Chin worked as linguist for the CIA's Foreign Broadcast Information Service, which monitors and analyzes foreign public press reports and broadcasts and translates classified information. An FBI agent testified this week that Chin had "access to all classified material, top secret and above."

Reagan did not mention specific cases today, and White House officials have refused to answer questions about the cases this week. Aides said espionage had been chosen as the topic of Reagan's weekly address because of the prominence of the spate of arrests in news reports.

"Some of you may be wondering if the large number of spy arrests in recent weeks means that we're looking harder or whether there are more spies to find," Reagan said. "Well, I think the answer to both questions is yes."

Reagan said his administration has given "high priority" to combating espionage and "we've had impressive results." He said the United States caught 13 spies between 1975 and 1980, but during his presidency has apprehended 34.

The president focused on Soviet-bloc espionage, saying: "We recognize that the KGB secret police and others seeking to exploit the openness of our society are not 10 feet tall. Neither, however, are they midgets. We're up against aggressive people who take their job seriously."

He added that recent arrests "should alert us to the danger we face. Even skeptics should recognize how necessary it is to maintain our top quality counterintelligence efforts."

While Reagan talked again today about reducing the number of hostile intelligence agents in the United States, he did not elaborate, and a White House spokesman said proposals for doing so were under study. Reagan broached this idea in an earlier radio address on espionage this year but later said he also was concerned about possible retaliation by other nations against the United States.

Among other measures Reagan cited today in describing the U.S. response to spying were "better monitoring of exchange programs, improving government communications and personnel procedures, better analysis, expanding counterintelligence capabilities abroad, and ensuring the security of U.S. embassies and bases throughout the world."