Sen. Bob Packwood of Oregon, one of President Reagan's most vocal critics in the Republican Party, today opens what he describes as an open battle "for the soul of my party" with a five-day swing through early primary states in New England.

Packwood's schedule strongly resembles that of a presidential candidate, but he insists that he has no intention of becoming one.

He is going to New Hampshire, the first presidential primary state; Boston, whose television stations cover southern New Hampshire, and Maine, which has an early presidential delegate-selection caucus date.

The trip, he said in an interview last week, is "a political, but not a presidential, one" aimed at "spreading my brand of Republicanism hither and there.

"I want to tug my party back into the mainstream before it's too late," he said. "I'm trying to change its direction."

The White House has no official reaction to the trip, deputy press secretary Larry Speakes said. But Packwood's effort is hardly going unnoticed.

"When you talk about saving the soul of the Republican Party, that's a direct slap at the president," one administration strategist said. "I've thought for the last year and a half that Packwood wanted to run for president.

"He's going after the old Rockefeller group," the strategist added. "Packwood sees a void out there, and he feels he can fill it."

"This trip is no threat to anyone in the White House," Packwood said. He said his purpose is to provide a rallying point for other moderate Republicans, concerned about the party's rightward drift in recent years.

"If we all say, 'Let's do nothing,' and don't speak out, then there won't be any change," said the three-term senator, who is largely unknown outside Washington, D.C., and his home state. "Someone has to be the point-man. Someone has to bring these issues before the party."

Packwood, ousted last month as chairman of the National Republican Senatorial Committee, has frequently criticized the Reagan administration for alienating women and minorities and becoming "the party built on white, Anglo-Saxon males over 40."

But the trip, which begins with an appearance today in Connecticut, represents his most concerted and open challenge to Reagan and other conservative party leaders.

Packwood is to appear before some of the groups most unhappy with Reagan policies--women, environmentalists and Jews--as well as eastern establishment Republicans, long uncomfortable with Reagan.

The journey, he said, "is in no way designed to twist the tail or tweak the nose of the anyone in the White House." But moments later, he added, "I've got a lot of causes to talk about."

Among them are the Equal Rights Amendment, legalized abortion and the sale of sophisticated Airborne Warning and Control System planes to Saudi Arabia. He has become a favorite among feminists and Jewish groups for his opposition to Reagan policies on these issues.

Packwood is scheduled to meet with the editorial boards of three of the region's most influential newspapers--The Boston Globe, The Hartford Courant and the Manchester (N.H.) Union Leader.

He also is to meet with legislators at a gathering hosted by Elizabeth Hager, who managed John B. Anderson's independent campaign in the 1980 New Hampshire primary, and tour an iron works in Portland, Maine, with newly elected Rep. John R. McKernan Jr., a Republican.