American motorists can still expect possible gasoline shortages and long lines at stations this summer even though, as a senior Department of Energy official said yesterday, world oil markets "are about in balance now globally."

"We are on an apparent gasoline consumption binge in this counrty... We could have a very uncomfortable summer from the standpoint of lines," the official said at a background briefing for reporters at which DOE aides asked not to be identified.

Energy officials also said that the United States has achieved one-third of the 1-million-barrel-a-day reduction in oil consumption that President Carter and the 20-nation Internation Energy Agency have called for by the end of the year in response to the Iranian oil shutdown.

At the same time, DOE says that the United States can meet that goal and still import more oil this year-about 200,000 barrels a day-than the 8.3 million barrels a day it imported in 1978.

Officials also said that overall , DOE expects to achieve one-third of the 1-million-barrel-a-day savings through increased domestic energy production and two-thirds from measures to reduce oil consumption.

While world oil production both from the Organization of Petroleum Exporting Countries and non-OPEC countries is higher this year than last, despite cuts in Iranian exports, DOE says gasoline supplies will be tight because refiners have to build inventories of middle distillate oil for heat next winter. DOE officials say that U.S. oil inventories were down 200 million barrels during January and Febuary-stocks that must be replaced over the next months.

To ensure that heating oil stocks are built up, DOE said its Economic Regulatory Administration will, if necessary, mandate the ratio of heating oil to gasoline that refineries produce.

Under such a scheme, DOE could force a reduction in gasoline production-in effect causing shortages at the pump-to ensure that there is sufficient heating oil for winter.

During the 1973-74 Arab oil embargo, the Federal Energy Administration forced refiners to reduce gasoline output, creating additional gasoline shortages at service stations, in order to build up heating oil supplies.

Energy Secretary James R. Schlesinger has repeatedly told Congress that he does not want DOE to "overreact" to the disarray in world oil markets in the wake of the Iranian revolution.

DOE also said yesterday that, as a result of the latest round of OPEC price increases, including surcharges levied by individual producers, the average price of oil imported for U.S. refiners soon will be nearly $18 a barrel, compared with about $15 a barrel at the end of 1978.

Officials also said that while Iran recently increased its oil production to 4 million barrels a day-compared with 6.5 million when the shah was in power-it cannot depended on as a source of oil until Tehran's government becomes more stable