Thousands of partisans for and against the Shah of Iran began arriving in Washington yesterday for two days of unprecedented head-to-head street demonstrations calculated to uphold or discredit Shah Mohammed Reza Pahlavi when he arrives today for a state visit.

The blitz of competing parades, speeches, picketing,street theater, leafleting and general political hucksterism will foscus today on the White House where the shah is scheduled to meet President Carter, but other points including the Iranian embassy, the Capitol and the Lincoln Memorial are also targeted.

The stakes for both factions are high. The anti-shah faction, led by dissident Iranians students, wants to portray the shah as a ruthless dictator whose regime should not be supported by the United States, especially in light of the Carter administration's advocacy of human rights abroad.

The pro-shah faction, led by Assyrian, Armenian and other Iranian-related ethnic organizers in Chicago and Los Angeles, wants to neutralize the student's presence, extend a general welcome to the shah and thank him specifically for his recently announced liberalization of restrictions on the official use of the Assyrian language in Iran.

Hostility has increased between the two factions as the pro-shah forces have accused the students of being Communist-dominated and the students have claimed the Assyrian-Armenian demonstrations are being bankrolled by the Iranian government. Each side has denied the charges.

Unusually tight security has been clamped down around the White House and across Pennsylvania Avenue NW at Blair House where the shah and his wife, Farah, are scheduled to stay overnight.

In addition to normal detachments of District of Columbia, U.S. Park and Executive Protective Service police, 75 members of the D.C. Police Department's riot-trained civil disturbane unit are on standyby. Another 225 members of the department's special operations and traffic division are on restricted leave status and available for call.

The Secret Service has imposed the so-called 500-foot rule around Blair House, barring political demonstrations within 500 feet of a building used by a head of state. The rule has the effect of limiting demonstrations to the eastern hal fof nearby Lafayette Park and a portion of the sidewalk in front of the White House.

In a last-minute spurt of predemonstration activity yesterday, both pro-and anti-shah factions made appeals to the public for support and sought center stage attention from the news media.

A flurry of telegrams, many of them with identical wording, were sent to the White House in support of the shah. Copies of at least 30 of the wires were sent to The Washington Post.

Assyrian and Armenian groups from Chicago and Los Angeles have scheduled a series of receptions and banquets. One group, the Armenian Solidarity Friendship Committee, blanketed Congress and the State Department with invitations to a banquet and evening of folk music last night at the Sheraton Park Hotel. Organizers said about 2,000 people had accepted invitations, including a handful of congressmen and Foreign Relations Committee and the several members of the key Senate House International Relations Committee.

Mike Minassian, a coordinator for the Armenian Solidarity group, said many of the more than 600 supporters who flew in from Los Angeles will demonstrate today at the White House.

On the anti-shah side, Iranian students called a press conference to blast the shah's regime. The Joint Committee of Iranians Students, which is an ad hoc coalition of four separate student associations, said "The U.S. government, multinationalcorporate interests and the shah himself are presently engaged in an orchestrated effort to mask the reality of oppression in repression in Iran."

The Committee to Defend Political Prisoners in Iran, an organization consisting of many old-line Vietnam era antiwar figures of the 1960s, also at-attacked the shah.

In a press conference, well-known anti-war figures Philip Berrigan and Victor Reuther said Iran has replaced South Vietnam as the most repressive police state in the world with the support of the United States.

Richard D. McCarthy, a former Democratic congressman from New York who headed the U.S. Information Service in Iran from 1974 to 1976, told the press conference he resigned from his job because he could not agree with continued U.S. support of Iran.

Reuther, retired director of international affairs for the United Auto Workers and now honorary chairman of Amnesty International, U.S.A., described the pro-shah demonstrations here as a "PR snow job" and an "abomination" in which a "head of state is flying in his own brass band and cheering section."

Pro-shah organizers acknowledge that thousands of dollars from American and Iranian business interests have been funneled to Assyrian and Armenian ethnic groups in Chicago and Los Angeles to help pay for charter plane fares and hotel accomodiations here. They contend, however, that most of the several thousands demonstrators expected here are paying their own way.

The shah and his entourage arrived in the United States yesterday afternoon at Williamsburg, Va., and are due here this mornig. Security was tight in Williamsburg, and spectators were kept at a distance.

The shah has visited the United States several times in the past and each time been confronted by Iranian student protesters. Today's demonstrations mark the first time that a significant pro-shah crowd will also be present.