House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) and the chairman of the Democratic Congressional Campaign Committee have proclaimed public support of an Ohio Democratic congressman who is facing a serious primary challenge for backing President Reagan's economic program.

The praise from O'Neill and the pledge of financial aid from Rep. Tony Coelho (D-Calif.), the campaign committee chief, for Rep. Ronald M. Mottl drew an angry blast from the Cuyahoga County (Cleveland) Democratic party chairman, Tim Hagen.

Hagen, who is supporting Mottl's opponent, said he would challenge O'Neill and Coelho "to come to Cleveland and tell the 11.9 percent who are unemployed because of the Reagan policies Mottl supported" why they want the incumbent reelected. He said he would urge Democrats to withhold financial contributions from the Coelho committee.

Mottl, elected to the House in 1974 from a conservative blue-collar district, supported Reagan on the key budget and tax roll-calls in 1981 and was one of the Democrats rumored to be considering a switch to the GOP after the 1982 election. Coelho said yesterday that Mottl had promised he would vote for O'Neill as speaker at the start of the next Congress.

What triggered the county chairman's outburst was a page-one story in yesterday's Cleveland Press quoting O'Neill as saying, "I personally like Ron Mottl and admire his courage. He follows his convictions. My Democratic party has three or four different philosophies and, while some of his are not the same as mine, I admire anyone who stands up for what he believes."

The same story quoted Coelho as saying his committee would "contribute up to $25,000 and do everying we have to do to elect Ron to Congress."

Hagen had considered opposing Mottl himself but instead endorsed county commissioner Edward Feighan for the race. He phoned O'Neill aide Kirk O'Donnell and Coelho to protest the story, reminding both that they had urged him last summer to put pressure on Mottl to support O'Neill and the Democratic alternatives to Reagan's budget and tax plans.

"They ask us to try to get him back in line, and then, when he goes with Reagan, they come in and back him when we've got a candidate who supports the national Democratic party policies," Hagen complained. Feighan added, "I've been campaigning against his support of Reaganomics and now he says the speaker's comments show that issue isn't all that important."

O'Donnell said he told Hagen that, while the Cleveland Press had quoted the speaker correctly, it did not constitute an endorsement. He said O'Neill's policy is that "I don't endorse people in Democratic primaries, but I'm for every Democratic member of the House of Representatives and I support every Democratic member."

Coelho said the Democratic Congressional Campaign Committee would send Mottl the maximum $5,000 contribution the law allows for the June 8 primary and up to $20,000 more, if needed, for the general election. "Our job," he said, "is to reelect Democratic incumbents. Ron has promised me he will support us in organizing the House, and that is the critical vote as far as we are concerned. After that, we have a job of trying to persuade him and other members to support the positions the leadership takes."