More than 300 demonstrators were arrested yesterday in front of the White House, where they blocked entrances and taped messages for President Reagan to the iron fence in a peaceful protest designed to force changes in several U.S. policies at home and abroad.

The protesters, most of whom sat for hours in the blistering sun while U.S. Park Police laboriously made the arrests, were participants in the four-day-long April Actions for Peace, Jobs and Justice that concluded yesterday with the White House arrests and lobbying on Capitol Hill.

The April Actions group is a coalition of more than 80 organizations that have joined together to oppose U.S. intervention in Central America, domestic budget cuts, racial apartheid in South Africa and the nuclear arms build-up.

"Is Ronald Reagan going to listen? Of course not," Ann Braden, a veteran civil rights and antiwar activist from Louisville, told demonstrators gathered at the Lincoln Memorial for a march to the White House. "We're speaking to the people of this country."

Park police said they arrested about 250 demonstrators in front of the White House and charged them with blocking an entrance. Another 79 protesters were arrested by D.C. police and charged with disorderly conduct and obstructing Pennsylvania Avenue NW. Both charges are misdemeanor offenses carrying possible $50 fines.

Though the protests here are intended to focus on several foreign and domestic policy issues, yesterday's demonstrators appeared -- by their hand-painted signs and chanted slogans -- most concerned about growing U.S. involvement in Nicaragua and El Salvador.

"Our president has an obsession about intervening ," said the Rev. William Sloane Coffin, a Vietnam protest veteran who recently returned from his third visit to Central America and was arrested yesterday. He compared the upcoming vote on aid to the "contras" in Nicaragua to the 1964 Gulf of Tonkin resolution that preceded the Vietnam War.

Those arrested yesterday had volunteered to stage a peaceful "blockade" at the White House as an act of civil disobedience. They arrived at the Lincoln Memorial for a brief send-off shortly after 7:30 a.m., paused for a moment of silence near the Vietnam Veterans Memorial, and reached the White House about 9:30 a.m.

But what had been planned as a morning protest soon stretched into most of the day. Park Police did not begin arresting the demonstrators, who broke into four groups and sat down on the sidewalk in front of four White House entrances, until shortly before noon. And though there appeared to be nearly as many police officers on the scene as protesters, only a few officers were used to make the arrests, which were completed about 4:30 p.m.

Park Police officials said they were unable to make any arrests until someone was actually prevented by the blockade from entering the White House grounds.

Officials said it took so long to make the arrests because they needed to arrest, identify and photograph each person before placing them in police buses and taking them to the Anacostia operations office.

While the heat seemed to try the patience of some officers -- protesters who "went limp" or locked arms during arrests were treated more roughly than others, and several were grabbed by the neck or punched -- the demonstrators remained orderly in the sweltering 93-degree weather.

As a crowd of about 150 supporters shouted encouragement from across the street in Lafayette Square, the protesters continued to sing and chant for several hours, even after supplies of oranges and spring water ran out and their faces began turning beet red in the sun.

At one point, about 40 officers sat in the shade along the White House fence having sandwiches and cold sodas while three officers worked together carrying protesters one at a time to police transports. The police got through the day thanks to the water tanks in their vans and periodic deliveries of ice and sodas. Yet when friends tried to pass some cold sodas to one group of protesters in the late afternoon, a Park Police officer took the bag and threw it in the trash.