BEIJING, JUNE 10 -- A Foreign Ministry spokesman today strongly denied that China was selling arms to Iran and in an apparent reference to the United States, expressed "surprise" that unnamed "senior officials of a big power" had made such allegations.

Li Jinhua, in a weekly news briefing, repeated the Chinese government's position that Beijing maintains "strict neutrality" in the Iran-Iraq war.

"It is quite obvious that certain U.S. newspapers have kept on fabricating and spreading such irresponsible reports with ulterior motives," she said, referring to recent accounts from the Middle East that have appeared in some U.S. newspapers regarding an alleged $550 million arms-for-oil deal concluded last month between China and Iran.

"We have noted that recently senior officials of a big power have also made similar remarks on several occasions," Li said. "We are greatly surprised at that."

Although Li did not name "the big power," diplomats said she was referring to the United States. In the past few weeks, senior U.S. officials have criticized China's reported decision to supply Iran with the antiship Silkworm missile.

On Saturday, national security adviser Frank Carlucci, rejecting a Chinese denial, said the United States believes Iran already has about 20 Chinese-built Silkworm missiles and may eventually have twice that many. He said the missiles were coming from China.

Assistant Secretary of State Richard W. Murphy said last month that Iran had agreed last year to spend $700 million to buy the Silkworm missiles.

One western diplomat here expressed frustration with what he described as the growing gap between China's overall foreign policy image and ideology and its goal to earn income to modernize its armed forces.

"China has held itself up as a leader in world disarmament," he said earlier this week. "How can you say you're a leader and at the same time be a major arms supplier?"

According to a recent U.S. Congressional Research Service report, China, between 1983 and 1986, emerged as the fourth-largest arms supplier to the Third World, after the Soviet Union, the United States and France.

In April, Iran's ambassador to China acknowledged that his country may have obtained weapons from China, including missiles, but he denied that this was the result of any military agreement. He said the Chinese-made missiles were available on the "open market."

{Iran's parliament speaker, Hojatoleslam Ali Akbar Hashemi Rafsanjani denied in a speech that his country had obtained Silkworm missiles from China, saying that Iran had only missiles captured from Iraq in 1986, Deutsche Presse- Agentur reported.}

According to a report last week in the Kuwaiti newspaper Al Qabas, China signed an agreement May 23 with Iran to build four factories in Iran for ammunition, rockets and tank spare parts. In return, China would receive 28 million barrels of oil annually. The report was picked up by Deutsche Presse-Agentur, the West German press agency, and that dispatch appeared last week in a Hong Kong English-language newspaper.

The Kuwaiti report cited as a source Ali Ballout, a former editor of a London-based Arab weekly. According to the report, China also agreed to deliver to Iran an unspecified number of Chinese-made MiG19 warplanes, 200 tanks comparable to the Soviet-made T59, field guns, and SA2 and SA7 antiaircraft missiles.

U.S. sources in Washington have said the Reagan administration is debating whether or not to strike preemptively against the Silkworms if they are deployed against shipping in the Strait of Hormuz.

Another Foreign Ministry official confirmed today that China is considering a Kuwaiti request for assistance in protecting Kuwait's oil tankers from attacks in the gulf. The official said that "the departments concerned in China are studying the request" to lease Chinese oil tankers or to put Kuwaiti tankers under the Chinese flag.