Even if Iran restores its oil exports to levels that prevailed under the shah, the Energy Department says that world oil prices could increase to $25 per barrel by 1985 and $38 by the end of the century, not counting inflation.

This forecast, assuming "worst case" conditions, is offered in President Carter's Second National Energy Plan, sent to Congress yesterday.

Called NEP-II, the plan was sent up seven days later than required by law and with little fanfare.

The inch-thick document, comprised largely of previously released materials, offers no new dramatic policy declarations, but does detail anticipated effects on various income groups and regions of the president's decision to gradually decontrol domestic oil prices.

The analysis presents Carter's decontrol program in a generally favorable light. I indicates that during 1981 an average family in the Midwest will pay $40 more for gasoline, and a New England family $36 more.

A household with a poverty-level income (less than $5,000 a year) will pay $26 more in 1981 for heating oil than it would without the president's decontrol package. The average nationwide increase for heating oil will be $29 annually, the analysis says.

Other DOE findings:

Even if oil prices rise to $30 a barrel or more, it will take years to develop sufficient supplies of synthetic fuels to have any impact on the cost of oil.

Despite ambitious administration goals, solar energy will not solve the nation's energy problems before the 21st century.

Regardless of the Three Mile Island accident, the nation must increase its reliance on light water nuclear reactors, speed up nuclear licensing, and seek better reactor safeguards.