They are marching on Washington - pacifists, Nazis, bicyclists, chiropractors, Tibetan-Americans, coal miners, lesbians, bird watchers, Iranian students, blind people - a clangorous new army of protesters and dissenters.

They come in a small, often rag-tag groups, usually a few hundred strong, occasionally in the thousands, sometimes only a dozen, clamoring at the gates of Congress and the White House.

Their voices are many, their purposes diverse, their issues often obscure. They have replaced the massive, single-minded protests of the Vietnam War era with a jangling new babel of outrage against the government, against abortion, human rights abuse, the cost of living, air pollution, nuclear power and a hundered other issues.

"This is demonstration city," says George Rodericks, director of the mayor's command center, which monitors all political protest activity. "We've had a tremendous increase in both the number of demonstrations and the spectrum of issues."

Veteran police officials say the proliferation and increased diversity of demonstrations has been phenomenal in recent years. Demonstrations of varying sizes are a daily occurrence. The total number of demonstrators marching and picketing just on the White House sidewalk leaped from 3,000 in 1968 to almost 48,000 in 1977, according to an estimate of the uniformed division of the Secret Service. U.S. Park Police overtime pay due to demonstrations has increased four fold over the past 10 years. D.C. Police spent $5 million in fiscal 1977 alone shepherding hundreds of marches and protests throughout the city.

Who are the demonstrator? They are farmers, American Indians, religious fundamentalists, Marxists, Maoists, anarchists, anti-abortionists, pro-abortionists, women's libbers, anti-women's libbers, gays, senior citizens, marijuana advocates, ban-the-bombers and a broad assortment of foreign nationals who have seized on President Carter's pronouncements on world human rights to protest alleged abuse of human rights in their native lands.

Washingt* on has become center stage for international disputes. Loudspeakers in Lafayette Park fill the air with foreign tongues. Militant Iranian students march up Connecticut Avenue chanting "Death to the Shah" in Persian. Jews and Arabs shout defiantly at each other in counter-demonstrations on the Ellipse. Ethiopian demonstrators hand out mimeographed leaflets containing labored harangues about the Ogaden region and the Eritrean problem. The D.C. Police Department's files of parade permits bulge with applications from Haitians, Koreans, Pakistanis, Romanians, Ghanaians, Bolivians, Indonesians, Baltics and Bermudans.

"Every time the minister of state from some country comes here, we get a demonstration," said Deputy Chief Robert Klotz, commander of the D.C. police special operations division and a man who has walked probably hundreds of miles of downtown streets, accompanying demonstrators, coordinating traffic control, mediating curbside disputes and clearing up misunderstandings.

Demonstrations in recent years have ranged from the deadly serious to the frivolous and from large-scale parades involving thousands of participants to lonely, one-man vigils in front of the White House.

On July 9, 40,000 to 100,000 women (depending on which police estimate you have) marched on the Capitol to urge extension of the ratification period for the Equal Rights Amendment. A few days earlier, Strippers for Christ, a group of buxom, but fully dressed, women, handed out pink and blue plastic rosaries in Lafayette Park.

"Sometimes you begin to wonder where the legitimate First Amendment stuff leaves off and the old con artist bit begins," said George Berklacy, National Park Service spokesman and a longtime observer of demonstrations.

The July 9 ERA march competes in size with what has now become the annual anti-abortion rally at the Capitol. The rally, held each January since the 1973 Supreme Court ruling that legalized abortion, drew up to 70,000 participants last Jan. 23.

Most demonstrations are small, however, rarely numbering over a few hundred. Some of them also involve issues that may seem obscure or remote to the average passerby.

A group of about 20 Tibetan-American citizens recently conducted a protest march at the Capitol. Their complaints: the State Department insists on listing "China" rather than Tibet, in their passports as their place of birth.

On Aug. 4, a group of mimes protested near the Spanish embassy because of what they said is the unjust imprisonment in Spain of six fellow mimes.

The days of the simple slogan - "Stop the War" or "No More Freeways" - are disappearing as the issues behind contemporary demonstrations become more complex.

At a recent demonstration here during the Nuclear Regulatory Commission's deliberations on whether to suspend the construction permit for the controversial Seabrook, N.H., power plant, a man carried a neatly printed sign that said:

"Splitting atoms to boil water is like ringing a doorbell with a canon."

The proliferation of demonstrations in Washington is not indicative of greater unrest or militancy in the country, police and other observers believe. Those feelings have always been there, they say.

"I think the success of the antiwar demonstrations and the civil rights movement here has a lot to do with it," said Rodericks in the mayor's command center.

"Their actions were widely publicized throughout the country," he said. "People read about it and saw it on television . . . and they realized Washington (could provide) a format for other groups, too."

Rodericks noted that D.C. police have gained a reputation for handling large-scale or violent demonstrations smoothly and diplomatically.

"The demonstrators feel comfortable here," he said."They know they're not going to be trashed . . . They don't feel intimidated . . . When (Nixon era Attorney General John) Mitchell and company were here, they'd call in the marshals, the army, the police. It was very intimidating. We don't have that anymore. Rodericks and police officials also noted that several court rulings in the past decade have liberalized demonstration rules in the city, opening up the Capitol grounds for protests for the first time and expanding the number of demonstrators permitted in Lafayette Park and on the White House sidewalk.

The net result, as one police official put it, is vastly increased "First Amendment activity . . . and a lot more overtime for cops."

There are no exact figures on the number of demonstrations per month or per year (permits are issued by an overlapping bureaucray of D.C. and U.S. Park Police, and some demonstrations spring up suddenly without any permit at all), but the total number is enormous.

During 1977, hundreds of demonstrations, large and small, occured at four principal target areas: the Capitol grounds, Lafayette Park just north of the White House, the White House sidewalk and the Washington Monument grounds.

Secret Service police at the White House have the most precise statistics. In 1977, they said, there were 677 separate demonstrations involving 47,865 participants on the White House sidewalk alone - a piece of pavement measuring 34 feet by 746 feet but clearly possessing far greater symbolic dimensions.

In contrast, 10 years ago there were only 368 demonstrations on the White House sidewalk involving 3,037 participants, according to police figures.

The sidewalk crowd ranges from large groups of activists protesting labor, pollution, housing and human rights issues to lone individuals standing day after day in the sun, such as Eleodor Predescu, a neatly dressed Romanian refugee who says he is being trailed and harrassed by "demented Jewish communist doctors."

The pacifists want peace. Bicycling commuters want to overturn the ban on bringing bikes into government buildings. Chiropractors want their practice to be covered by national health insurance. Bird watchers want Maryland's wetlands preserved for nesting. The blind want the Federal Aviation Administration to let them carry their canes abroad airplanes.

Coal miners, farmers and truck drivers have come to town, occassionally blocking traffic or building entrances in protest against alleged inequities in their industries.

Homosexuals, including a group of radical lesbian mothers called Dykes and Tykes, have joined the ranks of minority protesters. Veterans, senior citizens, residents of rental properties all have asked for a better shake.

And there are the Iranian students - masked activists who conducted at least 24 different marches and rallies in 1977 against the White House, the Iranian Embassy and the Capitol.

Just last Friday, about 1,000 Iranian demonstrators chanting "Down with the Shah" marched to the Capitol, the Iranian Embassy and CIA headquarters in suburban Langley, Va., to protest U.S. involvement in Iranian affairs.

The Iranians wear color-coded masks to distinguish the various factions of the radical Iranian Students Association to which they all nominally belong.

But they say the real reason for the masks is to prevent reprisals by Iranian secret police agents lurking in the streets here.

In a broad sense, Washington as the nation's captial has always been demonstration city. It was teh focal point for various protests such as the women's suffrage demonstrations of1919, the Ku Klux Klan rallies of 1926 and the veterans' bonus march of 1932.

But with the greater mobility and affluence of American society after World War II, demonstrations became increasingly frequent. The first sustained and regularly organized demonstrations were spurred by the budding civil rights movement of the 1950s and climaxed with the 1963 March on Washington when 200,000 people heard the "I Have a Dream" speech of the Rev. Martin Luther King Jr. at the Lincoln Memorial.

Civil rights demonstrations, including related open housing and anti-freeway rallies, continued into the late 1960s, sometimes almost simultaneously with the black urban rioting that erupted sporadically after the assassination of King.

But the civil rights protests soon became overshadowed by massive demonstrations touched off by U.S. military escalation in Vietnam.

The antiwar demonstrations were characterized not only by their massiveness but by their singleness of purpose. The Vietnam conflict was an unpopular war that brought a wide cross section of America - Democrats and Republicans, socialists and capitalists, old and young, rich and poor - together in common cause to end the U.S. involvement.

The outpourings were mammoth: 250,000 for the "New Mobe" rally on the Washington Monument grounds in November 1969; 60,000 to 100,000 for the Cambodian incursion protest at the Ellipse in May 1970; 175,000 to 200,000 for the National Peace Action Coalition march on the Capitol in April 1971.

One of the last major antiwar demonstrations was the so-called Mayday civil disobedience action against the city during the first week of May 1971 when thousands of activists attempted literally to stop the government by blocking city streets. More than 12,000 protesters were jailed, most of them after "sweep" arrests that were later ruled illegal by the courts.

One element of society that did not join the antiwar movement in large numbers was the black population. Few blacks joined the ranks of war protesters, and King's hope of joining the civil rights and antiwar movements in a unified effort never developed into full reality.

The Poor Peoples Campaign, led by King successor, Ralph D. Abernathy in the late spring of 1968, was among the last significant civil rights actions here. Its Resurrection City of plywood ana plastic shacks in West Potomac Park soon degenerated into a sea of mud from incessant rains, however, and its domination by militant blacks alienated some white support, further crippling chances for a civil rights antiwar movement coalition.

At the same time, local black resentment of the largely white antiwar movement grew as demonstration after demonstration here left a wake of vandalism, police tear gas and frayed nerves.

The antiwar demonstrations sputtered out in the mid-1970s as the war wound down. Blacks and whites generally have continued to go separate ways since then but with a whole new variety of objectives and issues.

Black and whites occasionally merge their numbers in protest - as in the recent backlash to the Supreme Court's Bakke decision - but these occurences are uncommon.

One long-lasting demonstration is the continous daily Soviet Jewry Vigil in front of the Soviet embassy on the 16th Street NW.

Started in December 1970 in protest against the trial of dissident Soviet Jews, the vigil has been maintained seven days a week ever since. Groups ranging from fewer than a half dozen to 200 gather on the sidewalk across the street from the embassy at about 12:30 p.m. each day for a 15-minute silent protest.

With the exception of a bloody attack by club-swinging Iranian students near the White House last November, when more than 100 police and pro-Shah demonstrators were injured, demonstrations of the late 1970s have been relatively free of violence.

"The demonstrators today aren't so antagonistic to the police," said Deputy Chief Klotz. "They're generally a nicer crowd . . . Their beef isn't with the police but with something else."

The growing controversy around the safety and necessity of nuclear power for domestic energy may provide a partial peek into the future of Washington demonstrations.

Already the issue has spawned several large, loose anti-nuclear coalitions - most notably the Clamshell Alliance - that came to Washington in large numbers for the first time early this summer to protest the Seabrook, N.H., power plant.

Like the antiwar movement a decade ago, the anti-nuclear movement is drawing an increasingly broad base of support ranging from housewives and ecologists to back-to-nature advocates and radical alumni of the 1960s.

Nuclear power has replaced the war as a symbol of government excess and irrationality, says Clamshell leader Chuck Matthei, "and the NRC [Nuclear Regulatory Agency in downtown Washington] will be the Pentagon of the 1980s."