The governments of Iran and Japan today reached basic agreement that the National Iranian Oil Company will sell crude oil to Japanese importers at an average price of $30 a barrel, according to Japanese Foreign Ministry sources quoted by Kyodo news service.

The agreement was reportedly reached early today at a meeting in Tehran between Japanese Ambassador to Iran Tsutomu Wada and Iranian Oil Minister Ali Akbar Moinfar.

Japanese trading and oil companies are expected to resume negotiations with the Iranian oil company immediately on crude supplies to Japan in 1980, according to informed sources in Tokyo.

These negotiations were suspended this month at the suggestion of the Japanese government, since it allegedly feared that acceptance of the much higher price then being asked by Iran would irritate the United States in view of the continuing crisis over U.S. hostages in Tehran.

A source at the Japanese Ministry of International Trade and Industry was quoted today by Kyodo as saying that the Japanese government would continue to ask oil importers to conduct negotiations involving Iran with care.

Japan imported 455,000 barrels of oil a day, or about 10 percent of its oil imports, from Iran in 1979, Kyodo said.

The agency quoted a Japanese oil company source as saying that, for financial reasons, Iran would export a high volume of oil next year and that Japan would not have to worry about securing the volume it needed.

Saudi Arabian Oil Minister Ahmed Zaki Yamani, in an interview published today, repeated his prediction that 1980 will see an oil glut that halt soaring prices.

He told the West German newsmagazine Der Spiegel that there would be a glut of oil even if Iranian production, hurt by the exodus of Western oil technicians after the overthrow of shah Mohammad Reza Pahlavi, stayed at 3 million barrels a day.

Iranian Oil Minister Moinfar himself confirmed in another interview published today that Iran's oil production for 1980 would probably range between 3 million and 3.5 million barrels a day.