By Marty Graham

SAN DIEGO (Reuters) - A U.S. judge on Friday tentatively rejected Republican presidential nominee Donald Trump's bid to dismiss a lawsuit by Trump University students who said they were defrauded through its real-estate seminars.

U.S. District Judge Gonzalo Curiel in San Diego told a hearing he would take under consideration arguments on both sides in the case and issue a written ruling in the coming weeks.

The 2013 lawsuit, one of three over the defunct Trump University venture, was filed on behalf of students who paid up to $35,000 to learn Trump's real estate investing "secrets" from his "hand-picked" instructors. The plaintiffs have sought class-action status.

The cases against Trump University have regularly cropped up during the presidential campaign. Trump was roundly criticized in May when he accused Curiel, who is of Mexican descent, of being biased against him because of the candidate's pledge to build a border wall between the United States and Mexico.

Curiel, who was born in Indiana, is presiding over two of the cases, with one set for trial in late November. A separate lawsuit by New York's attorney general is pending in that state.

Trump's lawyers say Curiel should toss the 2013 California lawsuit on the grounds that the New York real estate mogul, though personally involved in developing the concept and curriculum, relied on other executives to manage Trump University by the time the plaintiffs purchased their seminars.

"By 2007, his involvement was fairly minimal. He was not the person running this company. He founded it, he established it and he went off and let other people run it. It's like any other celebrity endorsement," Trump attorney Daniel Petrocelli said during the hearing.

Trump's lawyers claim references in marketing materials to "secrets," "hand-picked" instructors or "university" were mere sales "puffery." According to the defense, there is no evidence Trump intended to defraud students.

Lawyers for the students say the wealthy developer conducted the marketing for Trump University more than anyone else, starring in and approving promotional materials.

They claim Trump University instructors were high-pressure sales people, not "professors and adjunct professors" as Trump touted, and that New York authorities told Trump back in 2005 to stop calling his unaccredited venture a university.

"Somehow, belligerence trumps substance," plaintiff's attorney Jason Forge said. "If we say it loud enough, forcefully enough, it becomes true. Well, it doesn't."

Trump owned 92 percent of Trump University and had control over all major decisions, plaintiffs' court papers say.

(Additional reporting by Karen Freifeld and Dan Whitcomb; Editing by Tom Brown and Jonathan Oatis)