Saying that blacks and Republicans are both minority groups that should "soar together," Sen. Lowell P. Weicker Jr. (R-Conn.) told black voters today that they had been abandoned by the Democrats and should consider voting Republican in November.

Weicker, facing a tough reelection fight this year, was the only major Republican politician to address the annual convention of the NAACP, which is wrapping up its week-long 73rd annual convention here today.

Two Democratic presidential hopefuls, former vice president Walter F. Mondale and Sen. Edward M. Kennedy (D-Mass.), have made major speeches this week. Much of the rhetoric from their speeches and NAACP leaders has focused on how to defeat Republicans in November.

Weicker's speech, which did not attempt to defend the Reagan administration, was received politely.

A Republican-related flap continued over statements by NAACP Executive Director Benjamin L. Hooks that Vice President Bush had been invited to address the gathering but refused, saying he planned to be in Africa. Bush was in Boston yesterday.

Bush's office has insisted that he was never invited to the convention, but NAACP spokesmen said today that Hooks would stand by his statement.

In a development that they found encouraging this morning, NAACP leaders announced that an agreement for increased employment opportunities and promotions for black employes had been signed with the Edison Electric Institute, which represents 250 privately owned electric companies, and the American Gas Association, which represents 200 gas companies nationwide.

The agreement calls not only for more black employes at all corporate levels, but also for more contracts by the utility companies with black-owned firms as vendors or subcontractors. No quotas or target dates have been set, but Hooks said he already had a commitment for 3,000 summer jobs for young people.

Weicker, in his speech, conceded that liberal Democrats such as Kennedy have "every right" to criticize the Reagan administration's record on minorities. "I have had plenty to say myself on that subject," he said. "But the White House is only part of the story."

He said that, in fact, the Democrats were abandoning the civil rights movement. "Minority Americans who were long ignored by Republicans have been abandoned by the Democrats," he said, adding that most Democrats, sensing the political gains are to be made elsewhere, have left the civil rights field.

"We are in a period--and it will last a long, long time--of delicacy and danger. Because most white, middle-class Americans believe they have paid their debt to decency, and they have reason to believe that--and they don't want to be dragged back to the table again--and they're not going to be, if I read the national mood correctly," Weicker said.

Pointing to his own positive record on civil rights votes, Weicker referred to the recent Senate vote on an antibusing measure that about half the Democrats supported. The measure was supported even more strongly by the Republican majority and is now being held captive in the House Judiciary Committee by Chairman Peter W. Rodino Jr. (D-N.J.).

Weicker demanded to know why blacks had not confronted the Democrats who supported the antibusing measure.

"Why didn't you draw the line?" he asked. "Having people walk all over you is the price to pay for not drawing the line. Politicians figure that if you don't care enough to fight for racially integrated schools, then you won't mind subsidizing segregated academies with your hard-earned tax dollars.

"If you think you can count on the Democrats in Congress to save your backsides on these issues any more than they did on busing, you're selling yourself short," he said.

Warning that "blacks cannot afford to be a one-party community," Weicker told the delegates, "Republican administrations have been in power 17 of the last 30 years. That is a political reality black Americans must face up to."

Then, making a final pitch for black support for Republicans in the November elections, Weicker said, "Soar together or be earthbound. Those are the options for the minorities in America known as blacks and Republicans . . . . When blacks go to the polls this fall, it is my hope they will judge the candidates not by their party label but by their character and commitment to justice."