Secretary of State George P. Shultz succeeded yesterday in assuring a group of senators led by Majority Leader Robert J. Dole (R-Kan.) that the administration has decided to send "effective" weapons to the anticommunist guerrilla movement fighting the Marxist government in Angola, according to several participants.

After a 70-minute meeting between Shultz and a dozen senators, Sen. Mitch McConnell (R-Kan.) said he was satisfied by the secretary's briefing on administration plans for aid to Jonas Savimbi's forces.

"I told Secretary Shultz . . . that I'm reasonably convinced that effective assistance can be provided to Jonas Savimbi and that it can be done without affirmative action by the Congress," McConnell said.

Several senator sources said they felt that an administration request for a resolution approving its covert aid plan for Savimbi was no longer appropriate, partly because opposition to it in the Select Committee on Intelligence had diminished.

They also said there was some uncertainty whether the resolution could clear the Senate Foreign Relations Committee, where the administration is battling to save its request for $100 million in covert military and humanitarian aid for the rebels fighting the Sandinista government of Nicaragua.

"One option is to simply discontinue public discussion and let the administration make the decision unilaterally of going ahead with the covert program in Angola . Frankly, I think they should go ahead and do it," McConnell said.

The United States called upon the Angolan government yesterday to seize the offer made Tuesday by South Africa to begin steps Aug. 1 for the holding of independence elections in neighboring Namibia provided Angola agrees to a timetable for the withdrawal of Cuban troops from its territory.

Calling the South African announcement "a significant and positive step," State Department spokesman Bernard Kalb said an "enormous opportunity" had been created for a breakthrough in the long-stalled, U.S.-sponsored negotiations between Angola and South Africa over the intertwined issues of a Cuban troop withdrawal and Namibian independence.

Some congressional sources expressed skepticism at the administration's claim that the opportunity exists for "rapid movement" toward a settlement and some were concerned that the State Department might be using the South African announcement as a pretext for delaying covert aid for Savimbi.

Kalb said the administration was sending Deputy Assistant Secretary of State Frank G. Wisner to the region to consult with various governments on the South African proposal. But a State Department source said Wisner still had no definite plans for talks with Angolan officials.

Meanwhile, Assistant Secretary of State Chester A. Crocker yesterday began a new round of regional talks with Soviet counterpart Vladilin Vasev in Geneva. The meeting is one in a series of exchanges on regional disputes Washington and Moscow agreed to hold.