The Rev. Benjamin Weir, one of seven Americans held by Lebanese terrorists, was released last Saturday after more than 16 months in captivity and was secretly brought to the United States, President Reagan said yesterday.

Announcement that the 61-year-old Presbyterian missionary was safely home with his family in the Norfolk area came after three days of rumors that Weir had become the second American released as the result of intensive U.S. efforts to intercede with Moslem extremists in Lebanon.

Reagan, who made the announcement during a trip to Concord, N.H., said he talked with Weir from Air Force One and found him in good health and spirits. "I'm happy for him and his family," the president said, "but I will not be satisfied and will not cease our efforts until all the hostages -- the other six -- are released. The vice president plans to meet with the families of the other six remaining hostages Friday when they will be in Washington . . . . "

Neither Reagan nor other U.S. officials would discuss details of Weir's release. A senior State Department official, who talked with reporters on condition he not be identified, said Weir had been set free and had not escaped. The official refused to elaborate, saying:

"To the extent that we may have thoughts about why he was released, we don't particularly want to talk about them because it may have relevance to the other six . . . . We want to conduct ourselves so we don't do or say anything that disrupts the process" of freeing the others. However, he and other officials hinted that Syrian President Hafez Assad, who was instrumental in arranging the release of 39 passengers and crew from the Trans World Airlines jetliner hijacked to Beirut in June, had a role in obtaining Weir's freedom.

Edward Djerejian, a White House spokesman accompanying Reagan, told reporters that the administration, with Weir's approval, initially had sought to keep his release secret out of fear that publicity might jeopardize the other six Americans. However, Djerejian added, the decision to make a public announcement was made after the United States learned late Tuesday that release of the six is not imminent.

Despite denials from the United States and Israel, it was widely understood that the TWA hostages were freed as part of an unspoken deal for Israel to complete the release of more than 700 Lebanese Shiite and Palestinian prisoners held at its Atlit prison.

Some U.S. officials have acknowledged privately that Assad subsequently became angry at what he considered the slow pace of Israel's moves to let the prisoners go. As a result, the officials said, Assad had rebuffed U.S. calls for him to use his considerable influence inside Lebanon on behalf of the seven other captive Americans.

According to the officials, that situation began to change after Israel sent the last group of prisoners home from Atlit early last week. While carefully skirting discussion of Syria's role, both the senior State Department official and Djerejian said that the Atlit release had produced an atmosphere more "conducive" to U.S. diplomacy.

Following Israel's action, Assad met in Damascus, Syria, last week with four top leaders of the extremist Shiite organization Hezbollah, or Party of God, which is believed to be holding at least some of the Americans in Lebanon's Baalbek region, which is under Syrian military control. Hezbollah is regarded as being more responsive to influence from Iran than Syria. But it also is susceptible to Syrian pressure, and Assad is believed to have played a key role in obtaining the release in February of another American captive, Jeremy Levin, who was Beirut bureau chief of Cable News Network.

Reagan made his announcement yesterday as he concluded a tax-reform speech in front of the New Hampshire capitol in Concord. Amid loud cheers, he said:

"I'm pleased to inform you, if you haven't heard, that Rev. Benjamin Weir, who was held hostage for 18 months in Lebanon, has been released." The White House later corrected his statement to note that Weir had been held for 16 months, since May 8, 1984.

Djerejian later read a statement that said in part: "Since the first American was seized, the president has been engaged in intensive efforts to liberate our citizens . . . . While there was not direct linkage between the Atlit prisoners and the freeing of our hostages, we have hoped that repatriation of the Atlit prisoners would improve the atmosphere in the region. We therefore intensified our efforts when the Atlit release occurred."

Those still being held and the dates of their kidnapings are William Buckley, 56, a political officer at the U.S. Embassy in Beirut, March 16, 1984; Peter Kilburn, 60, a librarian at the American University of Beirut, Dec. 3, 1984; the Rev. Lawrence Jenco, 50, a Roman Catholic priest, Jan. 8, 1985; David Jacobsen, 54, director of the American University hospital, May 28, 1985; Thomas Sutherland, 54, dean of agriculture at the American University, June 9, 1985, and Terry A. Anderson, 37, chief Mideast correspondent for the Associated Press, March 16, 1985.

There have been persistent rumors that Buckley might have been taken to Iran for interrogation and that Kilburn, who has a heart condition, may have died. However, the senior official said the administration believes that all six are alive.