A high-ranking Israeli official said yesterday that he believes Syria has the power to free seven kidnaped Americans still held by Shiite Moslem extremists in Lebanon, and he added that if the United States asks, Israel probably would try to help the seven by delaying release of some of its Lebanese Shiite prisoners.

Commenting on Syria's role in arranging Sunday's release of the 39 American hostages in Beirut, David Kimche, director general of the Israeli Foreign Ministry, said: "We believe that if the Syrians had really been so completely helpful as they've made themselves out to be over this latest episode, we believe they could have done something about the seven."

In a meeting with editors and reporters of The Washington Post, Kimche reiterated the official Israeli and U.S. positions that there was "no linkage" between the freeing of the Americans and Israel's timetable for releasing its Lebanese prisoners, most of whom are Shiites. Although another 300 of these prisoners were released yesterday, 435 are still held in Israel.

Kimche declined to discuss on the record the dealings and arrangements between the United States and Israel during the 17-day hostage situation. But Israeli sources said that during the initial stages, Israel was "very confused" by "different signals within the administration" about whether the United States wanted Israel to stand fast and continue holding its prisoners or let them go in accordance with the demands of the hijackers of TWA Flight 847.

The sources said the situation was clarified by a series of phone contacts between Israeli Prime Minister Shimon Peres and Secretary of State George P. Shultz. The sources also acknowledged that the impasse was broken last Tuesday when Syrian President Hafez Assad offered to take the "linkage" problem on his own shoulders by volunteering to give the captors of the 39 Americans his assurance that Israel would release its Arab prisoners if they freed the Americans. Assad said he would give this assurance unless the United States asked him not to, and Washington indicated that it had no objection, allowing this unspoken arrangement to go forward.

In his comments, Kimche made clear Israel's concern that Syria not capitalize on its role by improving its image in the United States. Referring to his talks here with Shultz and other senior administration officials, he said:

"I have the impression that the administration understands very fully the role played by the Syrians. I mean you could say it needs a thief to catch a thief, and it needs a regime like the Syrian regime sometimes either to initiate or to stop a terrorist process . . . . It did demonstrate the strength that a dictatorial regime can generate because it is a dictatorial and ruthless regime."

He noted that the remaining seven Americans, who have been captives for up to 17 months, are believed to be held in Lebanon's Bekaa Valley, which is "completely under the domination of the Syrian army and even more so under the domination of Syrian intelligence."

Stressing that he was expressing a "personal feeling" and "not an official Israeli position," Kimche added, "It's inconceivable to me that Syrian intelligence does not know exactly in which base, in which building and in which room I would say most of these people are being held . . . . The fact that they haven't done anything about them, I think, says more about their sincerity to help than anything else."

Kimche was asked about reports that Israel might hold back some of the Shiite detainees to give the United States leverage in bargaining for the remaining seven hostages. He replied:

"Having said there's been no linkage up to now, I presently feel sure that we would do that, provided this is what the American administration would want us to do."

"I don't believe that there has been such a decision taken yet because I don't believe that this is the sort of thing that can affect these extreme Shiite organizations," he added. "But if it would help, we will do it, I believe. And this is a personal opinion; this is not an official statement."

It has been generally assumed that, despite the denials of linkage, Israel will respond to the freeing of the Americans by quickly releasing its remaining prisoners. But Kimche, insisting that the prisoners were detained originally because of their complicity in terrorist activities, said that future releases probably will involve "much smaller groups" than the 300 sent home yesterday, and that the timing will be tied to Israel's ability to get an agreement for an end to hostilities in southern Lebanon.

An Israeli diplomatic source, who asked not to be identified, commented on "different signals within the administration" during the hostage impasse that raised questions about whether the United States followed a double-track policy in dealing with Israel.

"Frankly in the first few days, we weren't quite sure what the American administration was expecting of us," the source said. "On the one hand, we were hearing voices saying, 'Stand firm. Don't give back those detainees.' On the other hand, we were hearing different voices saying that these detainees are being held illegally anyway, with the obvious inference that one should give them back. And we were hearing American officials more or less hinting that it's time the Israelis understood that they should be given back."

"But I must say that this confusion lasted a very short time," he continued. "I think it took the American administration a few days to get the thing clear in its mind about how it wanted to play it . . . . They wanted to make it crystal clear there's no deal here between Israel, the U.S. and the hijackers. Because of that, they were rather slow to get into a real dialogue with us . . . . "

Referring to the statement late last week by a senior White House official that American Jews should pressure Israel to release its prisoners, the source said: "That was very damaging to the administration. And on the same day, and on the days before, we were getting equally clear messages saying exactly the opposite."