Paris — The man who heads one of the major energy forums in the Western world sees a three- to five-year ''cushion'' period ahead, in which the world economy can grow without a rise in oil prices.
Dr. Ulf Lantzke, executive director of the 21-nation International Energy Agency, sees a large spare capacity of oil amounting to between 7 and 10 million barrels per day (b.p.d.) through 1986-87.
But Dr. Lantzke, a West German lawyer and economist, also warns that oil consumers - car- and homeowners as well as industries and governments - cannot and must not relax now that the Organization of Petroleum Exporting Countries (OPEC) prices have gone down for the first time since it was started in 1960.
Consumers should keep on insulating their homes and buying smaller cars. The concept of ''conservation'' should no longer be promoted with the idea of ''sacrifice,'' but as a way to improve life.
''Insulation cuts down noise as well,'' Dr. Lantzke said, ''and as a European , I say that smaller cars are more comfortable, too.''
In an interview with The Christian Science Monitor at IEA headquarters, he was skeptical about the widely held view that there will be a further sharp fall in oil prices.
Prices would remain under pressure, however, and his concern was that generally lower oil prices and an upsurge in the world economy could encourage consumers to be profligate with oil once again, starting at the end of this decade.
''If we fall into the happy-go-lucky attitudes of the 1960s, that might well lay the foundations of new problems on the oil front,'' he said.
A question being widely asked today is whether and how fast an end to the world recession will send demand for oil shooting up again, thus pushing prices up as well.
Dr. Lantzke's view is a moderate one. ''We do not underestimate what renewed economic growth could do for demand,'' he says, ''but for the next three, four, or five years I don't see a real price threat.
''With the exception of a major political event in the Middle East [which could interrupt supplies], for the first time in 10 years oil as a constraint on the world economy won't exist. For now, spare capacity is enough to compensate for the loss of oil production in any individual Mideast country except for Saudi Arabia.''
Beyond the end of this year, Dr. Lantzke sees ''the beginning of an economic recovery.'' The climate, he says, already exists, with economic indicators in the United States and West Germany looking up, and companies beginning to plan for expansion again.
''Whether this will translate into (higher) demand, no one can say without a crystal ball,'' he went on. ''How strong will the world economy become? At what point will people's perceptions be that the recovery will last, thus causing inventories to rise again?
''I think that, in the next three to five years, there is enough spare oil capacity in the world to cope with even a brisk upturn.''
Dr. Lantzke's approach was a shade more relaxed than the IEA position of last October, when its 463-page study called ''World Energy Outlook'' warned of a new energy crunch in the 1990s. The study estimated world oil demand rising from 49. 5 million b.p.d. in 1980 to between 50 and 56 million b.p.d. by 1990, with supply lagging at 50 to 52 million b.p.d.
Since the study was published, prices have fallen and demand has dropped dramatically.
The IEA still says it is right about a gradual trend toward higher demand, and officials say the scenario of the study has been set back only by a year or so.
The view is controversial. Elsewhere in Europe, especially in the City of London, many economists and analysts see demand rising more slowly. They also have much less conviction that the new OPEC oil price of $29 a barrel and an overall production ceiling of 17.5 million b.p.d. can stick.
One sign in OPEC's favor is that British Petroleum Company Ltd., Britain's biggest oil company and a major North Sea producer, has softened its attitude toward a price-cutting war with Nigeria. BP chairman Peter Walters said March 17 he did not want to see a ''sudden collapse'' in prices or a price war with Nigeria, whose crude oil price at this writing was still 50 cents a barrel cheaper than Britain's.
The IEA is the industrial world's energy answer to the first OPEC price explosion in 1973. It was set up in November 1974 within the framework of the Organization for Economic Cooperation and Development (OECD) to encourage member states to avoid overdependence on imported oil, and to plan against major disruptions in supply.
Members are the US, Britain, Japan, Canada, Australia, Austria, Belgium, Denmark, West Germany, Greece, the Republic of Ireland, Italy, Luxembourg, the Netherlands, New Zealand, Norway, Portugal, Spain, Sweden, Switzerland, and Turkey.
The agency, a relatively small body with a budget of $10 million and a staff of 110, including 63 specialists, encourages development of alternatives such as coal, nuclear energy, and natural gas. It also publicizes energy trends and studies prices.
Dr. Lantzke took a low-key approach to the period ahead as he sat in shirt-sleeves in his office on the third floor of a building beside the OECD headquarters, in the fashionable 16th arrondissement in Paris.
He predicted a difficult six months ahead for the OPEC cartel. Oil companies have been using inventories instead of buying new oil. They still have plenty of stocks left: Before the interview, a regular IEA monthly assessment of oil demand estimated that IEA members held 102 days' worth of land-based oil stocks, up from 83 days in 1978.
OPEC has also suffered from the mild winter in the Northern Hemisphere. Dr. Lantzke estimated that it had knocked between 500,000 and 1 million b.p.d. from anticipated OPEC sales.
''Demand for OPEC oil will go up in May and June,'' Dr. Lantzke went on. ''In the third quarter of the year, demand will reflect what people see as the expected demand for the fourth quarter.'' That would help send prices up.
As for the 1990s, ''I am not as sure as some that a crisis won't happen,'' he said. However, there is a ''good chance that people will remember the 1970s'' and keep on conserving oil.
If conservation and investment in coal, natural gas, and alternative energies continue, ''we have a good chance of getting through the rest of the century without an energy problem.''
There was a danger that even lower prices would stop countries investing in alternative energies. Dr. Lantzke felt that even if the price fell ''several dollars'' below $29 a barrel, other energies would remain economical compared with oil.
The IEA would like to see development going faster even today. The main substitutes for oil are coal and nuclear plants, he says, with natural gas lagging somewhat because of uncertainties about producer-country policies (an apparent reference to Algeria, Libya, and the Soviet Union).
On nuclear energy, Dr. Lantzke was optimistic, despite slowdowns in demand and construction in both the US and Western Europe.
''The peak of opposition in Europe is behind us,'' he said. ''The nuclear question itself played almost no role in the recent [West] German elections. I don't think there is a fear in Europe that cheaper oil would mean the end of nuclear power.''
On coal, he said that liquefaction was not economic at the moment. The IEA had advocated that one or two large-scale liquefaction plants be built ''as an insurance policy,'' but it had not happened. The technology of burning coal needed to be improved to take more account of the environment.
Dr. Lantzke felt that environmental issues had to be kept in perspective: ''If you say that coal must be burned without smoke, for instance,'' he went on, ''coal won't be burned at all.''