Decontrol of U.S. oil prices will cost American consumers more and result in smaller increases in oil production than the Carter adminstration has estimated, the Congressional Budget Office said yesterday.

While some of the differences result from competing assumptions about the present level of world oil prices the CBO report is likely to give a boost to opponents of decontrol.

Yesterday House Democratic opponents of decontrol defeated an effort to water down Tuesday's decision to fight President Carter's plan to begin lifting controls on June 1.

The CBO said that Carter's proposal would cost an average family an additional $135 in 1982, the first year of full decontrol. If the Organization of Petroleum Exporting Countries raises its prices 10 percent a year between now and then, the added cost would be $175.

The administration put the higher cost at about $100 per household, but that was calculated using the present "official" OPEC price f $14.54 a barrel and assuming only a 7 percent annual increase. The CBO, more realistically, but still conservatively, added $1.20 to that since most OPEC producers are charging at least $1.80 more than the official price.

Added oil output in 1985 from decontrol would be only 405,000 barrels a day, according to the CBO analysis, compared with the administration's estimate of up to 750,000 barrels a day.

The CBO and administration figures on the likely effect of higher prices in encouraging energy conservation were closer. The CBO pegged the potential savings at 215,000 barrels a day ing 1985, but with substantially great savings in the late 1980s and early 1990s. The administration estimated 250,000 barrels a day in 1985.

As the House Democrats reaffirmed their opposition to Carter's decontrol plan yesterday by all but formally adopting a resolution calling for an extension of controls, Energy Secretary James R. Schlesinger warned that pursuing such a policy could lead OPEC nations to raise their prices further.

If congress continues to oppose decontrol. Schlesinger told a meeting of House freshman Democrats, it would have a "detrimental effect on the attitude of OPEC countries." Specifically, he warned that OPEC nations might raise their prices at their June meeting.

Even the most cooperative of the oil-producing nations in OPEC have demanded "progress by the United States in terms of grappling with our energy problems," Schlesinger said. If the only act the United States takes is to block an adjustment of oil prices, "I think the reaction would be most unfavorable on the part of OPEC," he declared.

Meanwhile, President Carter warned, "Sof far, the American people have not faced up to the fact that we have an energy shortage that is going to get worse.

"We have an energy crisis," Carter said in response to a question during an interview with delegates to the annual convention of the National Cable Television Association in Las Vegas, which was carried by satellite from the White House Map Room. "We have shortages of oil. The shortages are going to get greater in the future and we're going to pay more for it."

Altogether, the CBO study found that decontrol would reduce demand and increase domestic production sufficiently to cut oil imports by about 620,000 barrels a day in 1985. The administration, on the other hand, with its different starting point on prices, put the import reduction at 950,000 barrels a day that year.

Despite the different estimates on the added cost to each family, both CBO and the administration think that decontrol will add about three-fourths of one percent to the inflation rate between now and 1982.

The White House yesterday supported a last-minute effort to derail the resolution calling for an extension of oil price controls.

But the Democrats refused to even consider the adminstration-backed substitute which called for delay of decontrol until Congress approves a stiff "windfall profits" tax.

The proposal was offered by Energy Subcommittee Chairman John Dingell (D-Mich.), Rep. Joseph Fisher (D-Va.) and others.

But the Democrats voted 124 to 96 to move directly to a vote on the resolution sponsored by Rep. Toby Moffett (D-Conn.) opposing decontrol.

A formal vote on the Moffett resolution may occur today. Moffett said he is working hard to get his supporters to "stay in town, stick with us. I'd like to close the airports," he said, refering to the fact that today is the last day of work before the Memorial Day recess and many members like to leave town early.

Moffett said of his resolution. "the message is clear. The anger of the American people is a much stronger lobbying force than the oil companies in the corridors right now."

But Moffett admitted it would be an "uphill battle" to get extension of controls adopted by the full House unless there is considerable Republican support, and said passage in the Senate would be even more difficult.

Meanwhile, House Republicans are expected today to call for a resolution of inquiry demanding the administration produce exact figures on current demand, oil supplies and the amount of oil being diverted to foreign countries. Scuh a resolution, if passed by the House must be answered by the administration in 15 days. CAPTION: Picture, REP. TOBY MOFFETT . . .urges backers to "stick with us"