From staff and wire reports

                  MEXICO CITY -- A standoff between Mexican authorities and striking
                  students at Latin America's largest university is continuing, with students
                  demanding the immediate release of colleagues arrested during clashes with
                  police.

                  The students of National Autonomous University (UNAM) fought with
                  police Wednesday morning, injuring at least 37 university workers under a
                  shower of rocks and firebombs. Police arrested 251 students.

                  "We cannot have a dialogue with the police in our classrooms, with hundreds
                  of our comrades under arrest," said Rodolfo Hernandez, a student.

                  Interior Minister Diodoro Carrasco said late Tuesday that university
                  authorities requested the assistance of the Federal Preventive Police (PFP)
                  after strikers attacked UNAM workers and anti-strike students who were
                  occupying one of its preparatory schools.

                  First direct police action on the campus

                  Wednesday's arrests represented the first time police took direct action in
                  the conflict since students went on strike last April, at first to protest a
                  proposed tuition fee increase to some $69 per semester from a token two
                  U.S. cents.

                  Officials dropped the fee increase proposal in the early months of the strike,
                  but a small band of radical strike leaders broadened demands for reform at
                  UNAM to include greater rights for the poor among the university's 270,000
                  students.

                  University authorities said the students are being manipulated by leftist
                  guerrilla organizations, but an analyst disputed that notion.

                  The students, according to Ignatio Rodriguez Reyna, were acting out of
                  frustration rather than ideology.

                  "They know even if they have some superior education they wouldn't have
                  any future ... it creates a social frustration," he said.

                  Violence endangers 'strategy of seeking dialogue'

                  The police action was notable because UNAM is self-governing and
                  off-limits to security forces unless university authorities request their
                  help.

                  It also marked a possible change in the willingness of authorities to use
                  force despite painful memories of a 1968 massacre by the army of students
                  demanding democracy.

                  But political analysts said the PFP action did not mean that force would be
                  used to a greater degree to take back UNAM's sprawling campus from the
                  strikers.

                  "I don't get the impression (what happened last night) was part of a greater
                  plan," said political commentator Sergio Sarmiento. He said he did not
                  believe that UNAM dean Juan Ramon de la Fuente was looking for an
                  excuse to send in the troops.

                  But a political analyst said the violence is bad news for those who hoped for
                  further negotiations to end the standoff.

                  "This has braked the ... strategy of seeking dialogue," said Joel Estudillo of
                  the Mexican Institute of Political Studies.

                     Mexico City Bureau Chief Harris Whitbeck and Reuters contributed to this report.