In these days of heightened concern over security, the arrival of a personal bodyguard has become a tip-off that an important official soon will be putting in an appearance at an embassy function.

So it was last night when U.N. Ambassador Jeane Kirpatrick arrived at the new embassy on Van Ness Street NW to join in the celebration of Israel's Independence Day.

With the fragile peace in the Mideast threatened by the Syria-Israel confrontation over Lebanon, the national holiday was observed against a backdrop of tension. Kirkpatrick, who had flown down from New York for State Department consultations yesterday and a Cabinet meeting today, said that she had heard the reports the Syrian soldiers may have crossed the Israeli-set "red line" in southern Lebanon.

"I heard the reports as I left New York, but they were still unconfirmed," the ambassador said.

On the observance of Israel's 33rd anniversary of its founding in 1948, Israeli Ambassador and Mrs. Ephraim Evron invited nearly 1,000 guests for the birthday party at the new embassy building. They arrived in two shifts at the embassy, the first to be built in the Northwest chancery section.

High walls enclose the new building, and last night security measures were strict: Each guests was checked before being admitted.

Among the invited were leaders of the Washington Jewish community and representatives from the White House, the State Department, Congress, the diplomatic community and the press.

Egypt was the only Arab country that came to join in the celebration of Israel's independence, with two representatives from the Egyptian Embassy in attendence.

"Egypt is the only Arab nation with whom we have diplomatic relations," an Israeli official pointed out, adding: "Anyway, the Libyans would be packing."

The Reagan administration has ordered the expulsion of members of Libya's diplomatic mission here on charges of provoking and supporting acts of international terrorism.

When asked about the expulsion order, Kirkpatrick replied: "Of course I agree with what my government does."

Kirkpatrick says that she remains "enormously enthusiastic" about the Reagan administration and her post as this country's spokeswoman at the United Nations. But she does find her life has changed drastically from her academic days as a professor at Georgetown University.

"It isn't that the hours are longer," she observed. "But as an academic, I did most of my work at home, just moving downstairs. Now I'm in New York in the morning and Washington in the afternoon."

And she has found that the nature of her work at the United Nations means that she must focus on "one or two aspects" of a problem rather than taking a more sweeping academic view.