Consumer prices soared by a seasonally adjusted 1 percent last month, the same large increase they registered in May after being basically unchanged during the first four months of the year, the Labor Department reported yesterday.

And while consumers' costs were rising, their earnings were dropping 1 1/2 percent in June, the Labor Department said yesterday.

Higher prices for gasoline and houses caused more than half of the price increase, the department's Bureau of Labor Statistics said.

Medical prices, which continued to rise even after most other consumer prices began a dramatic slowdown last fall, advanced by 0.9 percent in June, about the same rate at which they have been gaining all year. The rate of increase in food prices slowed.

For the first half of 1982, consumer prices went up at a seasonally adjusted annual rate of 5.1 percent, "rising from an annual rate of 1 percent in the first quarter to 9.3 percent in the second," the Labor Department said.

Even with the May and June increases, at an annual rate of more than 12 percent each month, consumer prices are just 7.1 percent higher than in June 1981, a marked improvement over the prevalent double-digit inflation of recent years. The consumer price index itself was 290.6 percent of its 1967 average, which means a basket of goods and services that cost $100 in 1967 cost $290.60 last month.

Robert Ortner, chief economist for the Commerce Department, said the May and June increases are a blip and no indication that double-digit inflation has returned to the U.S. economy.

"The May and June increases are at least as out of line" with the underlying trend of inflation as were the small increases in January and February and the small decline in consumer prices during March and April, he said.

Ortner said he thinks the underlying rate of inflation is between 5 and 6 percent and could be even smaller a year from now.

Gasoline prices rose 5.4 percent last month and 0.9 percent in May. The price increases were due in part to a reduction in the oversupply of oil that existed earlier in the year and to last spring's apparent agreement among Arab oil producers to cut their production to keep prices up.

That glut, caused mainly by a decline in oil demand because of the recession, contributed to a steady decline in oil prices from the middle of last year through April.

Recently, however, the price of oil and gasoline has levelled off, and Arab producers, many of them in need of more oil income, were unable to reach a new agreement on reducing production. That should keep oil prices at least level for the short term, experts said.

Treasury Secretary Donald T. Regan called the 1 percent increase in the CPI "more or less in line" with the administration's expectations because of the lagging impact of rising energy prices on the index.

"I don't look for that kind of jump any more from energy prices," Regan said yesterday. He agreed with Ortner on 5 or 6 percent inflation for this year, and, when asked if that meant smaller monthly increases for the rest of '82, replied, "Yes."

Even with the gasoline price increases in May and June, total transportation costs have risen only 4.6 percent during the past year.

House prices rose an adjusted 2.3 percent last month, following a 2.6 percent increase in May. Even though mortgage interest costs fell slightly, the total cost of a mortgage rose because the house price increases forced homebuyers to take out bigger home loans, according to John Wetmore, an economist with the Bureau of Labor Statistics.

Food prices rose 0.6 percent last month, after rising 0.8 percent in May. Food costs for consumers are about 5.1 percent higher than a year ago.

Clothing costs rose only 0.1 percent in June after declining the same amount in May. Over the year, apparel prices have risen 2.7 percent. Medical costs have proven resistant to the recession and are 12 percent higher than in June 1981.

Gross average weekly earnings for U.S. workers were $266.70 in June, compared with $265.52 in May. But seasonal adjustments bring those figures to $266.57 in June, down from $266.99 in May.