New and old Republican governors offered their party suggestions for success today that ranged from a full-scale attack on President Carter's policies to an avid courtship of minority and labor union votes.

William P. Clements Jr., the first Republican governor in Texas' history, said he had made Carter an issue in his race and had won votes by vowing to do all in his power to "deny Texas to him in 1980."

Govs. William G. Milliken of Michigan and James R. Thompson of Illinois and governor-elect Richard Thornburgh of Pennsylvania all cited their own success with black voters as an example the national GOP should follow.

The Republican governors, meeting here for their annual conference, celebrated the expansion of their numbers from 12 to 18 in the Nov. 7 voting, but worried aloud that their party may not have absorbed the lessons they think it needs to learn.

Some of the best things going for the Republican Party are right here in this room," said Milliken, winner of a third term in normally Democratic Michigan. "But let's not delude ourselves. It would be premature to claim that our victories signaled any real resurgence to the Republican Party nationally."

"It was a mistake in 1976 for us not to make a greater appeal to minorities and a greater effort to address the problem of the cities," he said. "And I must say in all candor that I think our party across the country has learned very little on this issue . . . As a party we have yet to offer real hope to urban Americans and a real commitment to the revival, or even the survival, of our cities large and small."

Milliken said he had doubled his share of the black vote from 1974 to 1978 - taking more than one-third of it this year - by a concerted effort to help solve Detroit's problems. He carried Wayne County (Detroit) without reducing his margin in the suburbs and rural areas, showing, he said, that attention to urban issues need not harm Republicans in their own political bases.

Thornburgh, who overcame a 900,000 registration deficit to win the Pennsylvania governorship, said he had captured 58 percent of the black vote and 50 percent of union members' support against Democrat Pete Flaherty.

Thompson of Illinois said he had used the same techinques of street and church campaigning successfully in Chicago's black wards, and Ohio Gov. James A. Rhodes said he had scored well in Cleveland by providing tax relief for businesses that brought permanent jobs to inner-city neighborhoods where, he said, "40 to 50 percent of the young people cannot find work."

Their testimony was an implicit plea for Republicans to choose a presidential candidate in 1980 who would campaign for and appeal to urban and minority voters. But direct discussion of presidential politics was muted at this first GOP gathering since the midterm election.

Miliken, Thompson and other GOP moderates talked of working together to keep the party from "veering to the right," as Milliken put it, but no outline of a concerted strategy appeared beyond vague talk that several of the governors might run as favorite sons in their own states.

Clements commanded attention in part because his surprise victory in Texas over Attorney General John Hill (D.) broke a century's Democratic monopoly on that governorship and in part because of his agressive campaign attacks on Carter.

Citing polls taken for his campaign which he said showed Carter has only a 26 or 27 percent favorable rating in Texas, the former Pentagon official said, "He was in trouble in Texas before I got elected and he's in more trouble now. I'm absolutely committed to denying him Texas," which Carter carried in 1976.

Clements said he had personal ties and political obligations to four potential 1980 GOP candidates - former president Ford, Ronald Reagan, John B. Connally and George Bush - and would remain neutral among them. He said he hoped Texas would have "an open primary" and threatended to file a court suit if the Democratic controlled legislature attempts to change the law permitting Republicans to hold a presidential primary in 1980.

While most of the governors were restrained in their predictions about 1980, Iowa's Robert D. Ray said, "With our new governors in Pennsylvania and Texas, the Republican Party now has the governorships of five of the seven largest states in the Union. And this will be a tremendous assest for us as we rebuild for the next campaign."