House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) made one more try Wednesday night to steer Jimmy Carter off a confrontation course with Congress, urging the Democratic President not to veto three potentially costly pieces of pending legislation.

During a dinner meeting at the White House the speaker tried especially to dissuade the President from vetoing the upcoming Labor-HEW money-bill, the legislation that provides funds for most of the social welfare programs dear to Democratic constituencies.

O'Neill told the President, who is 12 years his junior and a quarter-century his junior in Washington politics, that he might be sustained if he vetoed two other measures in dispute - a money bill for water projects Congress wants and Carter doesn't, and a farm bill with higher price supports than Carter wants.

But O'Neil also warned the President that, on the symbolic HEW bill, his veto might be overridden.

As O'Neil put it to reporters yesterday, he said to Carter, "I did not think there was any way we could override most of those vetoes if they come. We can't override the dams. But possibly we could the HEW veto."

The President invited O'Neil to the White House Wednesday evening to talk over differences that appeared to be leading to a Congress-versus-White House confrontation.

O'Neil came prepared for a serious evening of discussion, armed with statistics showing that none of some 25 vetoes during the Kennedy and Johnson administrations were of major legislation.

At the dinner, the two leaders were joined by 9-year-old Amy and Chip Carter with his wife, Caron.

After winner, Carter and O'Neil talked for 35 minutes with Chip present. Finally the two men conversed alone for 20 minutes, according to a White House spokesman.

A House aide said yesterday that O'Neil told Carter that the Labor-HEW bill, with money for traditional Democratic Party programs that help the poor and under-privileged, should not be vetoed by a Democratic president.

As approved by the House Appropriations Committee, the measure has $1.4 billion more for HEW than Carter asked for.

The overall tone, of the Wednesday talks, an O'Neil aide said yesterday, "was that everything is down the road. There is plenty of time to work things out and that negotiations toward that end should be under way."

The House is scheduled to vote on the water projects June 13 and Labor-HEW June 15.

O'Neil has said he sees no way either of those bills could be changed on the House floor to make them more suitable to the President.

On both measures, however, Republicans are planning to offer amendments that would support the Carter administration positions.

Rep. Silvio O. Conte (R-Mass.) said yesterday he will propose that 16 of the 17 projects Carter wants ended be eliminated from the public works appropriations bill.

Conte said yesterday a White House aide had asked him "three or four weeks ago" if he would co-sponsor such an amendment with a Democrat, but "They have not called me recently."

The Conte amendment is expected to fail, according to House Democratic aides.

On the Labor-HEW appropriations, House Minority Whip Robert H. Michel (R-Ill.) is expected to offer an amendment to cut about $500 million when that measure reaches the floor.

Again, Democrats are not expected to support the GOP move even though it would bring the measure more in line with Carter's request.

The Senate may drop several water projects but is expected to add to the House Labor-HEW bill rather than cut.

White House staffers, particularly in the Office of Management and Budget, are strongly pushing for a labor-HEW veto.