A third delegation of American physicists canceled plans yesterday to visit the Soviet Union, bringing to 43 the number of physicists who have called off Soviet trips to protest the recent jailing of dissident physicist Yuri Orlov.

The latest delegation to cancel was a group of 15 high-energy and nuclear physicists who were to leave on June 21 for a one-week seminar at the Joint Institute for Nuclear Research at Dubna, which is outside Moscow. The delegation included Nobel Prize Winner Owen Chamberlain of the Uninversity of California at Berkeley and was to be led by Dr. Benson T. Chertok of American University and Dr. Ernest Malamud of the Fermi National Accelerator Laboratory outside of Chicago.

"Because of the recent closed trial and harsh sentencing of our high-energy physics colleague Yuri F. Orlov, we shall not attend this conference," read a cable sent yesterday to Dubna and harsh sentencing of our high-en U.S. delegation. "We feel at this moment the climate would not be conducive to creative joint work and discussions."

The conference would have been the fifth to be heavily attended by Americans to discuss the problems of high-energy physics, which concern themseleves with the enormous energies generated by the acceleration of sub-atomic particles.

Besides the 15 Americans, one German Physicist invited to attend the seminar by the Soviets cabled his cancellation. He is Dr. P. Soding of the Deutsches Elektronen Syncthrotron in Hamburg. Eight European and Japanese physicists declined to join in refusing to attend the seminar.

Before the 15 canceled yesterday, 28 American physicists had called off scheduled trips to the Soviet Union to protest Orlov's jailing. One delegation of 20 cancelled on May 20, a second group of six canceled on May 25 and two individual physicists called off private trips to the Soviet Union.

The latest cancellations throws a monkey wrench into a joint high-energy physics project conducted for the last three years by Amercian and Soviet physicists at the Fermi accelerator outside Chicago. The two groups were to have written their final report at the end of the Dubna seminar. That report has now been delayed indefinitely, said American University's Chertok.

"It involved as many as 10 Soviet physicists who had been living with their families at Fermi for as long as two years," Dr. Chertok said. "The final writing of the paper is now up in the air."

The latest cancellation throws a monkey-wrench into a joint high-energy physics project conducted for the last six years by American and Soviet physicists at the Femi accelerator outside Chicago. Five experiments were completed by the two groups but only one was published and only two of the last four written in draft form before the Russians went back tot he Soviet Union.

"I had planned to talk to my Soviet colleagues about the two in draft and the two not written up while I was the Soviet Union," Fermi's Malamud said. "But that's delayed indefinitely now."