Secretary of State George P. Shultz, reporting on his two weeks of shuttle diplomacy in the Middle East, told President Reagan yesterday that Soviet pressure on Syria is a major roadblock to the removal of all foreign forces from Lebanon, according to administration officials.

"We still have a lot of trouble with the Syrians, who the Soviets are pressing to stay in there, and Shultz made this very clear to the president," one official said. "He tried to put the best face on it he could with the press."

Shultz later told reporters that he was still confident that the troop withdrawal agreement he negotiated last week between Israel and Lebanon will bear fruit "in the end" with the removal of Israeli, Syrian and Palestine Liberation Organization forces from Lebanon.

Several hours before Shultz' plane landed at Andrews Air Force Base from his Mideast mission, Soviet Ambassador Anatoliy F. Dobrynin went to the State Department to see Shultz' deputy, Kenneth W. Dam, in the latest of an unusually fast-paced series of Soviet-American diplomatic meetings.

Dobrynin has been at the State Department at least three times during the past week. Tight-lipped officials would not disclose the reason for the meetings, but the Middle East was believed to be on the agenda.

Shultz, speaking to reporters after his hour-long meeting with Reagan in the Oval Office, said he has "heard reports" that PLO fighters are reentering Lebanon.

"I would say first of all that is a violation of the agreement under which they evacuated Beirut and I think we ought to take note of that fact," Shultz said. "Second, of course it is an unwelcome development--we want them to be moving out, not moving in."

Implementation of the agreement between Lebanon and Israel depends on the willingness of Syria and the PLO to pull their forces out of Lebanon. Israel has made this a condition for withdrawing its forces from southern Lebanon.

Shultz said yesterday that while "there are problems and difficulties, it is clear that there is a weight of opinion building up in the Arab world that this is the opportunity to bring about Israeli withdrawal from Lebanon, along with all foreign forces."

Even though Syria has been critical of the peace agreement, Shultz said "that's not really the question that we're asking. We're asking them to withdraw, and they have said over quite a period of time that they are ready to withdraw when the Lebanese ask them to withdraw, so these are not unrelated subjects but they do have some difference between them."

Shultz said he has "no doubt" that Lebanon will make a formal request for Syrian and PLO forces to leave the country, and he noted that the Syrians "didn't refuse to withdraw or anything of that kind" when he met with them, although they were critical of the peace agreement.

Questioned by reporters about Soviet influence on Syria to remain in Lebanon, Shultz noted that the Soviet news agency Tass had attacked the peace agreement between Israel and Lebanon. "But what the nature of discussion between the Soviets and Syria is, I don't know," he said.

Shultz said he had "the impression" from his talks in Syria, and the "history" of that country, that "these are very independent people and I doubt that anyone is telling them what to do."

In his Paris stopover earlier this week, Shultz urged the Soviets to "get on the side of peace" and use their influence with Syria to bring about withdrawal of Syrian forces from Lebanon.

Asked about reports of an evacuation of Soviet dependents from Beirut, Shultz said he accepts the Soviet explanation that they are leaving for the summer holiday. "This school year is over and that's what they said they are doing," Shultz said. "It is perhaps slightly early, but not too much."

The secretary detailed one of the "side letters" that are associated with, but not directly part of, the Israel-Lebanon peace agreement. He said the Syrians and Lebanese both view Syrian withdrawal as an unrelated matter to the peace agreement, but that Israel has insisted on simultaneous Syrian and PLO departure with its own withdrawal.

"You can't have it as part of the agreement for good reason," he said of the Israeli demand. "It is therefore part of the side letter which the Israelis wrote to us and which we acknowledged."