After a week of upheavel, President Carter gathered his White House staff around him in the East Room of the White House yesterday for a pep talk and to tell them he expects both competence and loyalty from them.

More than 300 people, virtually the entire presidential staff, were invited to the unusual session, which was telecast by closed circuit to employes who could not leave their desks.

During the meeting, the president expressed no regrets about the purge of his Cabinet or the ongoing reassessment of top administration and White House officials that has cause concern among White House personnel.

But according to participants, Center conceded that his dicission to extract mass resignation offers from the Cabinet and senior White House staff was subject to drama." Some officials of foreign governments thought the resignation offers meant the collapse of the government, he said.

Sources said the president also acknowledged that some criticism of him has been valid. But they said that, without specifically discussing his plans for reelection, he expressed optimism about his political future.

The meeting clearly was intended as a morale booster for Carter's staff, many of whom expressed bewilderment and concern during the upheaval of last week, when five members of the Carter Cabinet were purged or quit and hundreds of lower-ranking aides were subjected to a White House-ordered "performance evaluation."

The meeting was closed to reporters but later was described by a senior presidential aide who asked not to be identified.

The official said the president spoke of the process that led to last week's shakeup, of some of his hopes and concerns for the country and of what his staff could do to help him provide national leadership. The rest of the meeting, which lasted more than an hour, was devoted to questions, the official said.

According to the Carter aide, the president told his staff they should not fear the evaluation forms filled out by their superiors, calling this process both necessary and important. Carter reportedly said that he expected competence, hard work and loyalty from his staff and added that anyone who met those standards had nothing to worry about.

Other participants in the meeting said the president used words like "bright," "competent," "effective" and "loyal," and said that anyone who could not live up to those standards should look for work elsewhere.

Participants said Carter was not specific about changes in his staff, but said several times he intended to broaden the advice available to him. They quoted Carter as saying that the criticism he heard during the Camp David "domestic summit conference" was not new to him, but that he had refused to deal with it earlier.

The senior White House official said the president cautioned his staff about speaking critically of others among their friends. Carter reportedly told them that when they criticize a member of Congress the criticism is repeated and sometimes published, giving the appearance of an official white House view.

Sources said a similar session with several hundred presidential appointees from throughout the government will be held today.

Yesterday's meeting came at the end of the first routine day at the White House in weeks. White House press secretary Jody Powell, conducting his first normal news briefing in about a month, said Carter will hold a nationally televised news conference in the East Room of the White House at 9 p.m. tomorrow.

This will be a departure in both time and place. Almost all Carter news conference have been during the day, not during prime time television hours. They also have been in the more austere setting of the Executive Office Building auditorium.

Powell said some White House staff changes may be announced this week. But he said the top priority is being given to finding a successor to Federal Reserve Board Chairman G. William Miller, named last week to replace ousted Treasury Secretary W. Michael Blumenthal.