BEIRUT, JULY 7 -- Kidnapers of American journalist Charles Glass issued a videocassette here today in which the captive, speaking haltingly and under obvious strain, said he had been working undercover for the Central Intelligence Agency.

It was the first time that an American hostage here has said he was involved in espionage. But Glass' appearance and delivery suggested strongly that his statement was made under duress and both the White House and ABC News, for which he has worked, denied that he had an espionage role.

"I am Charles Glass," he said in the videotape, which was poorly filmed and barely audible in spots. "Many of you only know me as a journalist. But few know the truth. I used the press as a cover for my main job with the Central Intelligence Agency. . . . I collect information for the benefit of the CIA."

Glass, 36, wore a dark blue track suit and looked weary, with a stubble of beard on his face. He appeared to have some difficulty in moving his upper lip, suggesting he may have been beaten or struck across the face.

He appeared alone in the seven-minute videotape, which was delivered to a foreign news agency here. It was accompanied by a brief typewritten statement in Arabic from the Organization for the Defense of Free People, a previously unknown group that on July 1 claimed responsibility for kidnaping him.

The group's statement, addressed to "the free struggling people," made no demands or threats, but it underscored the message Glass' kidnapers clearly intended him to convey about the purported nature of his activities in Lebanon.

"We put forth to you these truths and some of the results of preliminary investigations into the case of the American spy, Charles Glass, so you will become aware of the extent of danger such individuals pose to our people," the statement said. It continued: "America has been and still is seeking to exploit us, enslave us and dominate us and to consolidate the grip of Israel and its assistants on our soil.

"Investigations shall reveal bit by bit all Zionist schemes that he was acting through and will also uncover all agents linked to him in this mission," it said. "We shall put this information in your hands so you, the people, may judge those traitors for yourself."

{White House spokesman Marlin Fitzwater denied that Glass had worked for the U.S. government or engaged in espionage for it and added, "The history of these kinds of videotapes suggests that they are often done under coercion and perhaps even with torture."

{State Department spokesman Charles Redman called the videotape "apparently another cynical attempt to manipulate public opinion." ABC News president Roone Arledge said in a statement: "It is well known that a hostage under duress can be forced to make false statements which should not be accepted as valid. This is such a case. The U.S. government has stated that Charles Glass never worked for them in any capacity. He is a journalist who worked for ABC News for many years."}

Observers here noted that the timing of the release of the videotape coincided with the first signs of a Syrian-U.S. rapprochement and could have been intended to further embarrass Syria. U.S. special envoy Vernon Walters left Damascus today after talks with President Hafez Assad.

The captivity of Glass, a frequent visitor to Lebanon and Syria who resigned his job as Middle East correspondent for ABC-TV last March to work on a book here, has angered the Syrian leadership. His seizure within a few hundred yards of a Syrian checkpoint in the first abduction of a foreigner since Syrian troops marched into Beirut last February to provide security has led Syria to push for his release.

Syrian military intelligence officials have been in close contact with Iranian-backed fundamentalist operatives of Hezbollah in an effort to free Glass.

The visit of Walters, looked upon with suspicion by Iran and groups linked to it in Lebanon, is the first thaw between Washington and Damascus since last October, when Ambassador William Eagleton was recalled to protest Syria's alleged involvement in terrorism. The depiction of Glass as an agent for the CIA would clearly be seen by his kidnapers as embarrassing to Syrian leaders, according to analysts here.

Glass was grabbed with his host, Ali Osseiran, and their driver, Suleiman Ali Suleiman, by three carloads of gunmen who intercepted their car. Suleiman and Osseiran, son of Defense Minister Adel Osseiran, were released on June 24.

In the videotape seen today, Glass appeared to be choking back sobs at times and his expression showed what seemed to be an element of surprise at what he was reading.

Glass, who is married to a Briton and lives in London with her and their five children, said he had been on secret missions ordered by the CIA. "As I am an expert on the Middle East, I have been on many secret missions to the area," he said, gulping between phrases and rarely looking up from the text.

"I collect information for the benefit of the CIA. For that I made secret missions. They ordered me to do them. I am not the only one who uses the press as a cover for those things. Many people work with the agency, use the same cover and some of them were arrested in some countries. I am one of them.

"I come back to Lebanon on secret missions from the office of the CIA in London. My plan was to get the last information in this area and how the last actions affect the Israel-Christian relations, and also to study the subject of presidential elections and measure the political election atmosphere and security also. Also we discussed some arrangements in the Lebanese Army."

Accusations that Glass was an agent for the CIA and was dabbling in internal Lebanese politics, changes in the Lebanese Army and Israeli involvement in Lebanon, resemble common conspiratorial theories here among those who blame superpowers for Lebanon's woes.

Glass said his mission was to "tie up relations between the Israelis and Christian society through Maronite leaders" such as National Liberal Party secretary general Dany Chamoun, a likely candidate for president in the September 1988 elections. Chamoun has just returned from a trip to Washington.

Glass said he met with top Palestinian officials during trips to southern Lebanon and discussed with them American recommendations for problems between Palestinian factions.

"I promised to meet them again, but I am now here and I hope to pass this period well. I want to send my love to all my family. I love you," Glass concluded.