Participating students are being offered T-shirts with the slogan ''The Truth Cannot be Silenced'' and cards to pass out to classmates Thursday - the day after the Day of Silence - declaring their unwillingness to condone ''detrimental personal and social behavior.''

The driving force behind the Day of Truth is the Alliance Defense Fund, a Christian legal group that has opposed same-sex marriage and challenged restrictions on religious expression in public schools.

The event is endorsed by several influential conservative organizations, including Focus on the Family and the Southern Baptist Convention's Ethics and Religious Liberty Commission.

Mike Johnson, an Alliance Defense Fund attorney from Shreveport, La., said organizers were unsure how many students would participate in the Day of Truth, but he expressed hope it would grow in coming years as more people learned about it.

Johnson said the event is meant to be ''peaceful and respectful,'' but he made clear it is motivated by belief that homosexuality is wrong. ''You can call it sinful or destructive - ultimately it's both,'' he said.

The event is designed as a riposte to the Day of Silence, which began on a small scale in 1996 and is now observed at hundreds of schools and colleges across the country.

Most Day of Silence participants go through the school day without speaking - a tactic that may draw attention to the isolation and harassment experienced by many gay students.

Since 2001, Day of Silence observances have been coordinated by the Gay, Lesbian and Straight Education Network (GLSEN), a New York-based organization that also has worked to support gay-straight alliances at high schools across the country.

Kevin Jennings, GLSEN's executive director, said he doubted the Day of Truth would gain a following and stature of any significance.

''The Day of Truth is . . . an effort by adults to manipulate some kids.''

Underlying the dueling events is a fundamental disagreement over the rationale for the Day of Silence. The Alliance Defense Fund and other conservatives say GLSEN's agenda is to broaden national acceptance of homosexuality.

''No one is for bullying and harassment,'' Johnson said. ''But that's cloaking their real message - that homosexuality is good for society.''