The nation's electricity bills will rise to new heights this summer, elevated by a combination of factors that may also produce rotating blackouts and brownouts in some areas, according to government and industry experts.

Major elements in the power crunch are:

Rising worldwide oil prices and decontrol of oil and gas prices domestically.

A nationwide shortage of low-pollution, low-sulfur oil in the wake of the Iranian oil cutoff.

The shutdown of 25 percent of the nation's operating nuclear power plants for varying lengths of time.

"Any one of these factors would have caused trouble, but all of them together is just disaster," said a California utility analyst.

Electricity bills across the country could rise 15 percent or more over last summer's levels, especially in Virginia, Florida and California where all three factors are present, according to a number of industry experts. The brownouts are possible mainly in areas heavily dependent on nuclear power, according to Walter Brown of the National Electric Reliability Council, a Princeton-based group which keeps tabs on power flows.

"The concern is that bit by bit we're being nibbled at, things are tightening down," Brown said. "As much shifting of [electricity] load as can be done is being done already."

Most of the ballooning bill will result from automatic pass-through of rising fuel costs rather than formal rate increases. Utility regulators are becoming less willing to grant the power companies' requests as consumer protest increases, but automatic fuel adjustment clauses are in effect in all but 13 states.

The utilities this summer will be passing along the recent 9 percent rise in the price of fuel oil by the Organization of Petroleum Exporting Countries. They will pass along the 50 percent rise in the price of low sulfur (0.3 percent) oil required in many states to be used as an antipollution measure. And they will pass along the costs of oil-fired and coal-fired power they have had to buy to replace cheaper electricity that was produced by nuclear power plants shut for repairs and safety problems.

"All we do is make and sell electricity," said Mike Segel of the Edison Electric Institue, the utility trade association. "The consumer has to pay for it."

Formal rate increases will contribute a share of the rise. Utility requests for rate hikes that were pending at the end of March totaled $4 billion, up 21 percent from the $3.3 billion that was pending at the end of March 1978, according to EEI figures.

"The companies feel obliged to come back more frequently to make up for what they didn't get before," explained Marvin Lauterbach, vice president of National Utility Services Inc., a New York consulting firm that advises business and industry on utility rate matters.

Another factor in the rise is the number of nuclear plant shutdowns that might extend through the summer.

In mid-May, 16 of the nation's 70 licensed units were idle for various reasons: five for repairs of earthquake-proof equipment, eight for technical and procedural changes ordered in the wake of the Three Mile Island accident in Pennsylvania and three others for individual problems.

Together they left a 13,034-megawatt gap in the national electricity flow, chopping off about one-quarter of nuclear power's normal 13 percent contribution to the total. May is traditionally a low-demand month for electricity, but summer air conditioning will mean the power has to be replaced somehow, mainly from oilfired plants.

Estimates of that cost range from $3.6 million to $5.1 million per day over a normal daily electric bill of about $230 million.

Several experts said the Virginia Electric and Power Co. is among the most vulnerable utilities. Two nuclear units (Surry I and II) were shut in March for earthquake-related improvements, and a third (North Anna II) that was expected to come into operation in June has been delayed at least until August by a three-month freeze on new operating licenses by the Nuclear Regulatory Commission.

Senior Vepco Vice President W. L. Proffitt said, "Any delay ... could seriously affect the company's ability to meet customer demands this summer."

Vepco last week requested a $62 million hike to cover rising fuel costs. That would raise the average bill to its one million customers by $4.43 per month, a spokesman said. Combined with a request made earlier, Vepco rates could be 30 percent more this August than they were at the start of last summer.

Vepco is also worried about getting enough low-sulfur fuel oil as are Consolidated Edison in New York and, the state of Florida. Environmental protection laws at both federal and state levels have steadily lowered the permissible amout of sulfur in utility emissions, but unfortunately a lot of low-sulfur fuel came from Iran. With that supply gone, prices on the good stuff from Venezuela have risen 50 percent over last year's levels.

Florida Power and Light Co. in March asked and got a temporary waiver of the law to allow burning of oil with 2.5 percent sulfur, and the feeling is that a crisis was narrowly averted.

New York's Consolidated Edison, the nation's largest utility with the highest monthly bills, asked for a similar waiver but did not get it. Neither did Boston Edison, the Delaware-Maryland-Virginia (DelMarVa) power pool, the United Illuminating Co. of New Haven, Conn., or others, according to the Edison Electric Institute.

Con Ed, required to burn low-sulfur fuel, blames that fact for most of its expected 16 percent rise in summer bills to 3 million customers, according to spokesperson Leandra Abbott.

In California, the closing of the Rancho Seco plant in Sacramento for Three Mile Island-related changes plus the unexpected delay in the operation of the Diablo Canyon facility will leave the state with less than a 4 percent margin of reserve power, according to Rene H. Males, energy analysis director of the Electric Power Research Institute in Santa Monica, Calif.

"That probably means outages here during the summer," he added.

The District of Columbia's Potomac Electric Power Co., which burns coal for 70 percent of its fuel and high-sulfur oil for most of the rest, is not anticipating any problems this summer.

"Prices are always a little higher because we have to meet peak demand with oil burning units," said Charles W. Nicolson, vice president for engineering services, "and our oil costs are up. But it won't be that much different because we don't use that much oil."

Most of the consumer anger over rising prices seems to have focused on the nuclear angle so far. Don Michak of the Nuclear Information Research Service, an anti-nuke resource center, said his group is urging citizens to jam the hearing rooms nationwide when regulators consider price hikes.

"The cost of power is a political question depending entirely on the response of the regulators," he said. "I don't think they'll be making those decisions if the hearing rooms are full of people who think they shouldn't."