Forecasts are mixed; America's saving ways with oil -- will the trend go on?

Almost 10 years ago, people weren't getting up at 5 a.m. just to walk the dog; they wanted to beat the crowds to the gas station. It was a common assumption - oil was running out. Americans were going to have to make conservation a way of life.

And they did. They drove smaller cars. They rode in more fuel-efficient planes. They insulated their homes. And they manufactured goods in more fuel-efficient factories.

Partly as a result, Americans last year used up 15.2 million barrels of oil per day (m.b.d.), compared with 18.9 m.b.d. in 1978, the peak year. And many economists believe that conservation has not yet played itself out. Oil consumption in the United States will only be slightly higher, at 15.9 m.b.d., by the end of this decade, says Tor Meloe, chief economist at Texaco Inc.

''We're coming back, but we're not going to get anywhere near the peak,'' Dr. Meloe says. ''Substantial conservation still lies ahead.''

That is an opinion shared by Meloe and other oil experts. But not all oil analysts are of the Meloe school of thought. Opinion varies on how much conservation lies ahead and how big a part it will play in demand.

''There'll be conservation yet; my argument is that the trends toward conservation are slowing dramatically,'' counters Charles Bishop, an economist with Marathon Oil. ''The incentive has reversed, because of (lower) oil prices and (rising) incomes.''

Dr. Meloe believes conservation is still a big factor because ''it takes a long while for industry and consumers to respond to price increases. . . . The major factor in the last two years in reducing petroleum demand has been price increases that occurred in '73-74.''

He thinks industry has accomplished only about 40 percent of all the possible conservation action it could take. And while consumers first respond by driving less, turning down thermostats, and insulating, more conservation is on the way as they buy new energy-efficient homes and new cars that get better mileage, Dr. Meloe says.

''The most improvement in automobile (fuel conservation) is probably still in the future. During the recession, there weren't many cars selling - (therefore) fuel-efficient cars weren't selling,'' comments Walter Dolde, senior economist at A. Gary Shilling & Co., a New York consulting firm.

Mr. Dolde, who recently completed a study on gasoline consumption, says auto fuel usage will decline 3 to 4 percent annually over the next several years. Although more miles will be driven, he reasons that the decline will occur because more of the cars on the road will be new, fuel-efficient ones and because Detroit will keep upgrading mileage.

But Marathon's Mr. Bishop disagrees. ''Detroit will make and sell more larger cars than previously thought.'' He doesn't think present government requirements for fuel efficiency will get in the way of bigger sales of large cars. ''I think federal requirements of fuel efficiency will go right down the pipes. I can't see Congress restraining Detroit, sacrificing all those jobs.''

Bishop thinks gasoline demand for the whole transportation sector will ''grow a little bit'' this year. Consumption will still decline in the long run, he says, but ''the decline will be much less than generally recognized.''

He also maintains that industrial conservation of oil will slow down now because it no longer makes economic sense to invest in efficiency equipment. ''Right now, energy prices and oil prices in real terms are falling, and interest rates in real terms appear very high. Capital is more dear, so there is little incentive for manufacturers to continue to substitute capital for energy.''

''One reason there are so many points of view (on conservation's future impact),'' says Warren Shimmerlik, ''is that no one has had this experience before and no one knows what to expect.''

Mr. Shimmerlik, an oil analyst and vice-president at Merrill Lynch, Pierce, Fenner & Smith Inc., sees oil consumption as having to do more with the economy than anything else. For the last two years, when industry was in the midst of a recession, oil cutbacks were not caused by conservation but by lower production output, Shimmerlik explains.

''The decline of use was not different from the decline of output,'' he says. Industry needed less, so it used less.

He sees the recovery taking US oil demand up in the next few years, and doesn't think conservation will play much of a role at that time. Some economists believe, in fact, that consumption will be higher in 1985 than in 1990. ''After the push from the economy, we will go back to the inexorable decline in demand,'' he says.

That leaves only a few options open to the oil industry, says George Friesen, director of the energy group at Chase Econometrics, a forecasting firm. Mr. Friesen says the major oil companies are not in a position to market to developing countries - where demand is highest - because of national oil companies already being in control in many of those places. So they will have to ''retrench'' to the industrialized nations, and the only way for an individual company to grow there will be ''by increasing market share at the expense of other companies, or diversifying outside of oil.''

Increasing market share means price cutting and cost cutting - two trends already going on. It has also meant reducing the number of refineries and going after crude, either through acquisition or exploration, that has low production costs. As for diversification, Friesen comments, ''It hasn't been too successful so far.''