The electric bills now being delivered to Washington area consumers are 27 to 40 percent higher than last year, setting a record high for July, according to utility company figures released yesterday.

Most of the blame was tied to the record hot July weather which prompted consumers to rely to a greater degree than usual on air conditioning. An average residential customer in Virginia, for example, used 932 kilowatt hours during July, compared to 768 in July last year.

The July bills are also higher, however, because of summer surcharges, higher fuel costs and recent rate increases.

The average Virginia consumer will pay $59.93 for electricity used during July, according to figures from the Virginia Electric and Power Co. (Vepco). That is 40 percent more than the $42.94 average bill for July 1979.

Bills for residential customers of the Potomac Electric Power Co. (Pepco), who live in Maryland, Virginia and the District of Columbia, are up 27 percent. The system-wide average price for last month was $45.72 compared to $35.87 for July 1979.

The increase caught some customers by surprise.

"We didn't think we had used our air-conditioning units that much," said Susan Niebling of Northwest Washington, whose family of three was billed $104.53 for the period ending July 26. That was nearly double the $66.36 bill they received for the previous month. The Nieblings live in an area served by Pepco.

Calls from Pepco customers about bills have "increased decidedly" since statements for July were mailed, a company representative said. She said Pepco received 5,000 telephone calls in one day, about 73 percent more than the same day last year. Many of the callers wanted to know why their bills were so much higher than usual.

But after reviewing the July averages, Pepco officials said the bills were lower than they had anticipated.

They said customer conservation kept the averages down.

"Despite the hottest July on record, the bills are not abnormally high, because people are using their air conditioners carefully and conserving energy," a company representative said.

About 50 percent of a consumer's summertime power bill typically goes for home cooling. The rest is for lighting, cooking, hot water heating and miscellaneous appliances.

Statistics from both Pepco and Vepco show that the average homeowner used more electricity during July 1977 than any July since then. The Vepco average was 1,025 kilowatt hours in 1977, compared to 932 this summer. Pepco's average was 826 kilowatt hours in 1977, compared to 788 this year.

However, the dollar cost of the average electricity bill this summer establishes a new record: $59.93 now for Vepco, compared to $49.60 in 1977, and $45.72 now for Pepco, compared to $40.94 before.

The increases in the cost of power result from:

Recent rate increases. Pepco rates went up 11.4 percent in the District in June, 4.5 percent in Maryland in April and 7 percent in Virginia also in April. Vepco rates in Virginia rose $18 million on April 1.

Summer surcharges. Under rate schedules in effect in all three jurisdictions, electric utilities charge more for power during the summer than during the winter. The summer surcharge varies from one area to the next. In Virginia, for example, a Vepco residential customer pays $6.36 more per 1,000 kilowatt hours of power from June through September.

Higher fuel charges. Both utilities have experienced increases in fuel costs which are passed through to customers in the form of the fuel adjustment. cThe District of Columbia customer has been hit hardest by the fee this summer.

The District fuel charge for July was 2.7 cents per kilowatt hours, compared to 1.9 cents for June and 1.03 cents for May. In contrast to that, the Virginia customers of Vepco are getting a break on fuel fees. A decrease of $5.30 per 1,000 kilowatt hours is in effect for July and August to compensate for customer overpayments of fuel charges earlier in the year.

The increases in utility fuel bills during the summer are caused by lower generating efficiency and peak customer demands for power. Energy officials often compare the utility plant straining to meet customer summer time needs to an automobile traveling at high speeds. The car moving at 85 miles per hour burns more fuel and is less efficient than when it is traveling at 55 miles per hour. The same is true of a utility that must turn on all of its generating plants -- including the older, less efficient units -- during hot weather.

In addition, some peaking units which are turned on only for those hours of greatest customer demand, use a more expensive fuel than the base oil-fired plants.

Vepco has been particularly hardhit this summer by customer need for power. To satisfy those needs the company earlier this week urged customers to conserve energy or face the prospect of brownouts caused by high conservation helps customers save money.

"The hot weather causes utilities to use their most expensive generating equipment," he said.