The University of Maryland in College Park granted degrees to aproximately 3,000 undergraduates and 600 graduate students yesterday in a commencement ceremony marked not by pomp but informality and color.

While all of the graduates came in black caps and gowns, there were almost as many variations on special features worn with the traditional uniform as there were graduates.

Some students wore plastic microscopes atop their caps, other "X"s and "O"s similar to those used to play tic-tac-toe, rainbow stripes, mirrors, alphabets, stuffed animals and balloons.

Then there were the signs: "Hi, Mom", "Thank God", "No More Money Needed, Dad, Boo-hoo."

And there were the champagne bottles carried openly by those who had worked hard over four years to gain reputations for hard parting.

The students, who sat in chairs on the floor of Cole Field House, acted sometimes as if they were attending a basketball or football game. They punctuated speeches by the most popular commencement guests with loud applause, confetti, and occasional shouts.

Katharine Graham, chairman of the board of the Washington Post Company and chief commencement speaker, won special applause when she told the group: "You are getting much less publicity for leaving here than Albert King [the university's all-American basketball player] did for deciding to stay."

She won their hearts when she remarked: "Some aspects of life today are so trouble and threatening as to bring to mind the apocrphal commencement speaker who said for those about to sally forth, he had two words of advice: 'Don't go.'"

In officially granting degrees, some of the college deans even took an informal approach. "The teachers tell me the students have learned enough. The students tell me they want to go," said Francis Stark, provost of the division of agricultural and life sciences. "All I can ask, chancellor, is let my people go."

The ceremony was not entirely informal though. Graham told the graduates and the 14,000 or so parents who attended that the heavy economic interdependence among nations that has developed in the last few decades will be a major factor in future world affairs.

"I am really convinced that what is needed is nothing less than an entire set of new economic relationships among the industrial and developing countries that produce oil and the consumer nations of the third world."

Among those who received honorary doctorates at the ceremonies were Graham; Frank Press, chief science adviser to President Carter; opera singer Rosa Ponselle; and painter Clyfford Still.