TEHRAN, AUG. 21 -- The Iranian parliament's speaker, Ali Akbar Hashemi Rafsanjani, warned today that "only one match can start a fire" in the Persian Gulf and charged that U.S. naval forces there have increased the danger of war.

"If war starts in the Persian Gulf, no one knows the proportion it will assume," Rafsanjani said in a speech at a prayer service. "So if your aim was to bring security to the region, you have only made it worse."

{Late in the day the third convoy of three reflagged Kuwaiti tankers escorted by U.S. warships reached the coast of Kuwait "without incident," a Pentagon spokesman in Washington said. The convoy had been delayed off Bahrain Thursday by high seas and winds.}

Rafsanjani, one of the Islamic republic's chief leaders, used the ceremony to address the Reagan administration directly, pressing Iran's campaign to prevent Iraqi warplanes from resuming attacks on Iranian oil shipments through the gulf. For the last several weeks, Ayatollah Ruhollah Khomeini's government has been warning that it will retaliate sharply against Arab shipping if the attacks are renewed as Iraq has threatened.

Expanding on these warnings, Rafsanjani said the U.S. naval build-up to protect Kuwaiti oil tankers constitutes "psychological terrorism" that could lead to a military conflict neither Iran nor the United States wants. Diplomats here also have expressed fear that U.S.-Iranian hostilities could begin through a mistake, a field commander's rash action or Iraqi military moves undertaken against U.S. advice.

"We do not want to confront the United States," Rafsanjani said. "We did not want to confront the {Iraqi} Baathist regime, either. We do not want a war to spread. But if war is imposed on us, we will defend ourselves, and there is no limit to what we will do."

{In Washington, the State Department said the Reagan administration is willing to hold high-level talks with Iran's deputy foreign minister, Mohammed Jawad Larijani, who is coming to New York next week for a United Nations disarmament conference. State Department spokeswoman Phyllis Oakley said, "We are not particularly seeking such a meeting but would be prepared to meet should the deputy foreign minister so desire."}

Diplomats said the Iranian government has decided to draw the line at any interference with its oil shipments, which account for more than 90 percent of foreign exchange needed to finance the seven-year-old war with Iraq. This policy has been complicated by the Reagan administration's professed determination to protect Kuwaiti and other Arab shipping, the likely targets of any Iranian retaliation.

Iraqi President Saddam Hussein has been reported as saying he will not renounce attacks on Iranian oil shipments, because they are an important way of reducing Iran's ability to wage war. In addition, observers here pointed out, Iran's campaign amounts to a demand that the Iran-Iraq war be restricted to the bloody struggle for territory, in which the larger Iranian forces hold an advantage.

The United States, according to Iranian officials, has pressured Hussein to hold back his Soviet- and French-equipped Air Force, citing the recent U.N. Security Council resolution for an immediate cease-fire. Iraq has accepted the resolution; Iran has not rejected it, but has criticized it as unacceptable in its present form.

Iraqi planes, meanwhile, have mounted several attacks against Iranian oil installations, but none against tankers. {Iraq announced air raids Friday on an aluminum plant and two other Iranian factories.}

Iranian officials have pointed to the U.S. entreaties to the Iraqis as proof that the Reagan administration is afraid of what Iran can do in the gulf. Rafsanjani, speaking to several thousand followers at Tehran University, repeated that theme today, saying the United States has been humiliated because it fears having U.S. warships damaged by mines.

"When the U.S. ships reached the danger zone, they stopped," he said, apparently referring to the delay of the third convoy. "They said it was a storm. It was the same storm that occurred at Tabas."

Tabas is the desert landing zone where American commandos seeking to rescue the U.S. Embassy hostages in 1980 were forced to abort their mission, losing eight dead in a helicopter accident.

{News services quoted Rafsanjani as charging that the United States "covered up" another mine accident to "one of their ships." A Pentagon spokesman denied the charge, saying no U.S. warship had hit a mine.}

Rafsanjani also struck out at President Reagan. He said Reagan's dispatch of military forces to the region showed he has lost control of his actions and become a danger to peace.

"Besides cancer of the nose, he has become uncontrollable," Rafsanjani said. "His speeches are written by others and he only reads them. Intelligence sources tell us Reagan has no control at all, and unfortunately there is no one to take his place."