Rep. Eugene V. Atkinson (D-Pa.), a maverick in his second House term from western Pennsylvania, intends to become the second Democratic congressman to switch parties in recent weeks, according to administration and congressional sources.

Atkinson, who supported Sen. Edward M. Kennedy (D-Mass.) during the 1980 presidential primaries, is expected to announce his decision today after a meeting with President Reagan, Transportation Secretary Drew Lewis and White House political aides, sources said.

On Sept. 24, Rep. Bob Stump (D-Ariz.) announced that he intends to change, and several other Democrats are said to be considering the move.

The switches come as polls are beginning to detect a drop in the new public support for Republican congressional candidates. Nonetheless, pollsters say the GOP is still in its best position in two decades.

Atkinson was unavailable for comment yesterday, and his office would neither confirm nor deny reports of the switch. The son of a steelworkers' union official, he represents an industrial district that the Pennsylvania congressional delegation proposed eliminating in reapportionment. The state is to lose two congressional seats.

Although an alternative redistricting plan advanced by GOP leaders in the legislature is favorable to Atkinson, a key administration official said "redistricting was never a factor in this. There was no deal made on redistricting."

Atkinson, 54, has an erratic and colorful political history. When first elected in 1978, he was so shocked by the high cost of housing in Washington that he lived in his House office, showered in the House gymnasium and ate his meals in the House cafeteria.

He was an early supporter of Jimmy Carter in 1976 and, as president, Carter spoke at a fund-raiser for Atkinson. But when Carter ran for reelection Atkinson became the only Democratic congressman in western Pennsylvania to endorse and campaign for Kennedy.

He was quoted as saying at one Kennedy fund-raiser that, "I have a loyalty and belief he Kennedy will provide the kind of leadership we need. I voted with Carter only about 25 percent of the time. Kennedy will bring the best minds in this country together."

Still later, Atkinson attended a meeting of Democrats flirting with the candidacy of independent presidential hopeful John B. Anderson.

Atkinson is a fiscal conservative who owned an insurance company and served as Beaver County, Pa., Democratic chairman before his election to Congress. He has been courted by the Reagan administration since last spring, when the president personally called Atkinson while he was appearing on a radio call-in show and persuaded the Democrat to support budget cuts.

Atkinson has subsequently supported Reagan on several key budget and tax-cut votes.

In recent weeks Atkinson has met with White House political advisers, Lewis, who was Reagan's Pennsylvania campaign manager, and several House Republicans, including House Minority Leader Robert H. Michel (R-Ill.) and Rep. John LeBoutillier (R-N.Y.).

Conversations with Lewis, widely respected for his knowledge of Pennsylvania politics, are said to have been the key to Atkinson's decision.

"In the end, it was a philosphical decision," one administration official said. "He is very comfortable with us philosphically."

Rep. Austin J. Murphy (D-Pa.), whose district abuts Atkinson's, said Atkinson last week denied that he would switch.

"I'll believe it when I see it," Murphy said. "I don't think it will fly very well with his constituents. If you go out and espouse the things Teddy Kennedy stands for one year and a year later espouse the things Ronald Reagan stands for, people start wondering."