A mob brandishing wooden clubs, brass knuckles and chains and shouting "Long Live the Shah" attacked a group of dissidents gathered for a lecture today at a university here.

The obviously orchestrated attack was the latest in a toughening crackdown of dissidents that began while Shah Mohammad Reza Pahlavi was conferring in Washington Nov. 15-16, a visit that provided violent anti-shah demonstrations there.

In those meetings, President Carter is seen here as having soft-pedaled his human rights policy toward Iran in deference to strategic and oil considerations.

The victims of today's attack - by about 100 men who wore street clothes and arrived in two matching green buses - identified the attackers as members of the Iran's feared secret policy, SAVAK. Both SAVAK and the Iranian Information Ministry declined comment.

Members of the mob physically prevented me and two other Western journalists from following the dissidents being chased away from Aryamehr University.

Other of the attackers forced two of the reporters into a taxi and ordered the driver to take them away from the scene of the demonstration.

At least a dozen dissidents were injured and a few were arrested later when two truckloads of riot police arrived. By then the attackers - most of them carrying identical rough-hewn clubs about two feet long were patrolling the street and chanting proshah slogans. None was arrested.

A clash Saturday was the most violent in the current crackdown against dissidents.More than 350 Iranian riot police wearing U.S. made helmets and armed with wooden truncheons invaded Tehran University and battered students, according to witnesses.

About 65 persons, including four professors, were injured and 100 students arrested. The attack came hours after the shah returned here from Paris, where he had stopped after the U.S. visit.

Today's incident occured after about 400 persons had gathered to hear a lecture on "freedom" by leftist writer Mahmoud Baharzin. But the gates were locked and a notice said the lecture had been canceled for the second consecutive day.

The dissidents milled around quiently in front of the university for about an hour and were dispersing when they were attacked. Some of the dissidents were cornered in alleys and beaten while others were kicked, club-bed and punched on the sidewalk.

Observers said the attack by plain-clothesmen-instead of uniform police - apparently signaled a shift in tactics. They said they expected the government to claim the incident was a clash between unruly extremists and patriotic pro-shah citizens. No by-standers joined the attackers or participated in their pro-shah sloganeering afterwards.

Not all of the dissidents were students. A middle-aged office worker, asked why he had come for the lecture, complained about repressive government policies and said "there is no law in Iran." He added that he felt he could no longer remain silent.

"The knife is on the bone," he said.

A professor, commenting after Saturday's attack at Tehran University said, "They were beating everybody." His shirt was still stained with blood from having helped students to safety, including a French scholar who repeated "I am French" as he lay bleeding from a headwound. The university infirmary was full of other battered students, another witness said.