The traditionally Democratic, big-city-oriented U.S. Conference of Mayors is to end its 47th annual convention here Wednesday with the selection of a Midwest Republican as its new president.

Mayor Richard E. Carver, 41, of Peoria, Ill., will take over as the new conference president after a proforma vote approving his selection by the organization's nominating committee. He will become the fourth Republican president of the group since its founding in 1932.

When he goes before the convention Wednesday to accept his new post, Carver plans to tell his fellow mayors - especially the liberal Democrats - that they have nothing to fear. His acceptance speech says, in part:

"People might expect that one of the first Republican mayors to be president of the U.S. Conference of Mayors would present a different approach to solving the serious problems that confront our cities. They might expect that such a mayor would even present a different version of what these problem are.

"My concerns, however, are not partisan. Nor am I convinced that contemporary urban problems present suitable material for valid partisan discussions."

"That speech summarizes may position," said Carver, who will be succeeded as vice president of the organization by Mayor Richard G. Hatcher of Gary, Ind. "My concern is first for the needs of the cities, I expect to act on the basis of those needs and not on the basis of party," Carver siad.

However, Carver conceded that when his party needs him, he is usually willing to act. Thus, when fellow Republican mayors asked him to be present Monday at a news conference held to criticize President Carter, Carver showed up.

"I didn't agree with everything that was siad at that news conference. But I wasn't going to snub the Republican mayors," he said.

Besides, Carver added, criticism of Carter also has come from some Democrats attending the five-day session, such as Chicago Mayor Jane Bryne, whose scathing attacks on the president stunned Republicans and Democrats alike.

The conference consists of 800 manyors of cities with populations exceeding 30,000. The membership is broken down as 50 percent Democrats, 30 percent Republicans and 20 percent independents.

Carver, who has been mayor of Peoria since 1973 and says he will run for the Senate in 1980, describes himself as a "moderate conservative." He said that though he disagrees with the president on a number of issues, "I will support him 100 percent in the areas where I agree with him." One such area, he said, is the president's effort to involve private business in urban development.

"If you're going to meet the social needs of the cities, you've got to have jobs and economic development. The only way you can get those things is through private investment," said Carver, who also heads a family-owned lumber company.

Carver has won national recognition for his work in bringing together public and private dollars to successfully combat slum conditions in Peoria, population 126,375.

Carver noted with irony that his city was the butt of may jokes during the Nixon administration, when administration aides popularized the slogan "Will I Play in Peoria?" The reference was to the city's supposedly simple virtues and simple faith, and to its symbolism as the heart of middle America.

"We had half the world's media wandering around my city when Nixon was president," Carver said," but the Nixon people were right, whether they knew it or not. We do have a cross section of America in my city. As a matter of fact, corporations constantly use us in their test marketing.

Confirming his intent to run for the senate next year, Carver said: "I know that it isn't doing anything and that it is responsible for many of our present problems. But I think it will be a challenge. I enjoy doing something where you can find satisfaction in involvement." CAPTION: Picture, RICHARD E. CARVER . . . group's fourth GOP president