As a brisk wind swept through Lafayette Square near the White House yesterday morning, a small contingent of pet owners huddled around the Rev. JOHN C. Harper, who had called his congregation and their animals together for an unusual ceremony: the blessing of pets.

A couple of weeks ago, a church in Fairfax Station, Va., had called forth its congregation to bring tools to be blessed.

If tools, why not dogs and cats, said members of St. John's Church, located on 16th Street NW across from Lafayette Square.

So the animals were blessed, while elsewhere in the city the routine of a soft autumnal weekend unwould: joggers jogged, Easter Seal Walkathon walkers walked, Iranian protesters protested and fundamentalist Christians fulminated.

Back at Lafayette Square, Father Harper told the crowd of about 50 pet owners to form a line and tell him the name of the beast to be blessed.

Some appeared to require more than a blessing. "What my dog needs, Father, is more like an exorcism," said Carl Nelson, a congregation member who lives on Capitol Hill. Staring coldly at his ankle-high mutt, Nelson said, "She's a terrible dog. She barks at me when I come home late. She even bites me."

"Bless you," Father Harper told the dog.

There was a cat, a few poodles, terriers and hounds and several more canines of mixed breeding.

By way of explaining what this was all about, the congregation sang "All Things Bright and Beautiful," which thanks God for making "all creatures great and small."

Meanwhile, from Franklin Park at 13th and K streets NW, about 300 supporters of the "Anti-Imperialist, Anti-Reactionary Committee of Iranian Students" marched several miles to the Iranian interest section of the Algerian embassy at 2139 Wisconsin Ave. NW, carrying placards reading, "No more executions in Iran" and "Down with Khomeini, long live revolution."

Down on the Washington Monument grounds, a congregation of about 100 Christian supporters of the U.S. March for Victory Committee gathered to hear the Rev. Carl McIntire, a perennial protester here, preach against the evils of Communism.

"We want a new beginning in the battle against Communism," the fundamentalist minister told the group. "We plan to reject communists wherever they show their faces."

McIntire's group shared the grounds with numerous tourists and a country fair style picnic staged by public television station WETA which celebrated its 20th birthday yesterday.

U.S. Park Police estimated about 700 persons participated in yesterday's fifth annual Easter Seal Walkathon through Georgetown and other parts of Northwest Washington.