For almost 5,000 students at Howard University, Catholic U. and the University of the District of Columbia, yesterday was graduation with a strong measure of traditional ceremony and some exuberant cheers that light showers did not mar seriously.

At Howard it was the 111th commencement; at Catholic, the 90th; and at the UDC the second. The academic festivities were elaborate at each.

For the University of the District of Columbia, whose classroom buildings are scattered around the city, graduation for 1,290 students was held at the D.C. Armory.

Secretary of Labor F.Ray Marshall, the main speaker, used the occasion to denounce inflation as a "very deep problem" that threatens poor Americans more that anyone else.

"As people scramble to beat inflation," Marshall declared, "the poor will suffer most - first because they are least able to change their buying habits or increase their income - but also because inflation can jeopardize public support of programs that the poor depend on."

"Inflation is much more than an economic problem," Marshall said. "It is a force that pits people against each other - that undermines our generosity and compassion - that eventually bring out the worst in a society."

Marshall stressed that Carter administration efforts to reduce inflation will not involve cut-backs in government programs for the poor, ill, and elderly."These people are the victims, not the causes, of inflation," Marshall declared.

Howard University held its commencement in its stadium, conferring degrees on approximately 2,000 students and giving honorary doctorates to five.

It was a day for luminaries. The main address was given by Sen. Edward M. Kennedy (D-Mass.), who spoke critically of the Carter administration's energy policies.

Just before speaking, Kennedy was awarded an honorary doctorate of laws.

"It has taken me 23 years to get from Harvard to Howard," Kennedy declared after university President James E. Cheek conferred the award. The crowd cheered.

There also were cheers for singer-actress Lena Horne, who received unhonorary doctorate of humane letters.

The other honorary degree recipients were Louis E. Martin, special assistant to President Carter and former president of the Chicago Defender; Clarence Mitchell Jr., longtime Washington lobbyist for the National Association for the Advancement of Colored People; and Richard L. Terrell, former vice chairman of the board of General Motors Corp.

As Cheek conferred degrees enmasse on graduates of each of the different colleges, the ceremony became festive.

Liberal arts students were asked to stand first for recognition, and cheered themselves warmly. Pharmacy was next, and threw confetti. Nursing shrieked with glee and released white balloons. Business administration chanted, "We're No. 1."

With appropriate solemnity, divinity students did not cheer, whom Cheek called on them to stand.

There were similar scenes at Catholic University, which held its commencement for 1,707 graduates on the steps of the National Shrine of the Immaculate Conception.

The main speaker was Livingston L. Biddle Jr., chairman of the National Endowment for the Arts, who stressed the values of "imagination, awareness, and vision" as the most important goals of education.

"That is perhaps education's greatest gift." Biddle said, "the development of the eye, the ear, and the mind so that each can become . . . an imaginative individual, a special person."