Former Delaware governor Pierre S. du Pont IV pointedly angered a group of liberal and moderate Republicans meeting here today by joining a conservative attack on their organization and renouncing many of its leaders' positions.

Edging closer to a bid for the presidential nomination, du Pont set out to ally himself with the conservative wing and separate himself from the Mainstream Republican Committee, a group with strong ties to the liberal Ripon Society.

Du Pont, who said in an interview he expects to decide this summer about a presidential bid, described himself to the group as "someone most of you believe shares your views. After all, where should an eastern Republican named du Pont expect to be standing?"

But he said he endorses military aid to anti-communist movements in Nicaragua, Afghanistan and Angola, rejects the notion that the Pentagon should accept "its 'fair share' of spending reductions" and favors additional tax cuts.

Rep. Jim Leach (Iowa), chairman of the Mainstream Republicans, said afterward: "He made a decision to be a George Bush look-alike and a Jack Kemp stand-in, and he has done that very well." Asked what he thought of the du Pont speech, Leach said: "It's his right to say what he wants."

Mary Louise Smith, former head of the Republican National Committee and a vice chairwoman of the conference here, said du Pont is "making an appeal to a certain segment of the party," referring to the right wing. She said his speech reflects a skewing of the Republican presidential selection process "by the influence of the far right."

Du Pont was the only prospective presidential candidate to show up here, although Vice President Bush sent two members of his political action committee staff and is paying for a breakfast for all participants on Sunday.

Before speaking to the group at lunch, du Pont attended a news conference called by a local conservative group, the United Republican Fund of Illinois, where such figures as Rep. Henry J. Hyde (R-Ill.) and Max Hugel, chairman of Project '88, attacked the Leach group's use of the name "mainstream."

"The premise of the mislabled 'mainstream' group is that the Republican Party must embrace liberal policy in order to become the majority party," Hugel said. "The premise is fatally flawed."

Du Pont was not as severe as the other conservatives in his criticism of the Mainstream Republican Committee, but he argued that Republicans have succeeded not because "we sought the 'mainstream.' We sought good ideas . . . . The so-called mainstream is beginning to wash over us. It should not lull us to sleep."

Leach said the conservative attack violated the American principle of allowing competing groups to meet. Leach also reiterated charges that the conservatives sought to undermine the gathering by warning presidential candidates that they might be criticized if they attended. Steven Baer, executive director of the United Republicans, denied the charge.