A lovely spring day brought out the political activists in Washington yesterday and incidentally provided a view of the heterogeneity of American life.

Under a bright sun shortly before noon, members of the National Organization of the White House to demand passage of the Equal Rights Amendment.

They left to make room for more than 100 Veterans of Foreign Wars who paraded, many in uniform to protest what they believe is the abandonment by President Carter of the men still listed as missing in action from the Indochina War.

Across the street at exactly the same time another group of about 100 people much younger and many barechested, sprawled on the grass in LaFayette Park, listened to poetry and sang in a show of solidarity against a different target: Anita Bryant, the singer and orange juice promoter who is leading a fight in Florida to get a law guaranteeing homosexuals equal rights repealed.

The two groups appeared oblivious not only of each other's cause but also of each other's presence.

Across town a fourth group, composed mostly of inner-city blacks, gathered by the banks of the Anacostia River in a day-long commemoration of Malcolm X Day complete with music and speeches.

The mood was strictly upbeat. This is the sixth year the event has been held and Malik Edwards, the coordinator of the Malcolm X Day Committee, explained the importance the fallen leader has for black youngsters.

"Malcolm X set an example of a person who is 'a criminal' under the system and proved that you cannot go so far down that you can't come up and become a contributor," Edwards said.

Barbara Sizemore, a candidate for an at-large seat on the City Council and one of the scheduled speakers, said Malcolm X is an example at a time when the power structure is retreating on its promises of equal rights and equal opportunities.

"The example that he gives is one of individual willingness to struggle the ability to confront the power structure and make meaningful demands to that power structure of the improvement of the quality of life for black people."

The veterans who paraded in front of the White House demanded that President Carter veto Vietnam's entry to the United Nations unless that country agreed to setting up an inter-investigate the condition of men still listed as missing inaction.

"Our government has decided to take the word of a pack of murderers and is giving everything away," Tom Kaiser, a veteran from Long Island, said.

The veterans argue that there are many Americans of the 1,300 listed as missing in action who are still alive. They want the international commission to bring these men to a "free zone" where they can be asked whether they want to remain in Vietnem or come home.

"The Commander-in-Chief is not willing to stand up for the men of the armed forces." said George Brooks of Newburg, N.Y., whose son Nicholas has been missing for seven years.

"I'm supposed to assume he's dead because I haven't heard from him lately," Brooks added. "Well, it's pretty hard for him to get in touch with me."

Brooks and other veterans said the government has evidence that many of the men are still alive but refuses to release it.