Acceptance and rejection letters from the University of California have started to course through the mail, making March a typically nerve-wracking month for high school seniors. But this year, there's a big difference.

The university expects to reduce enrollment by as many as 3,200 UC-eligible students to cope with the budget crisis. So some students who in years past would have been guaranteed a spot in the UC system will have only the option of attending a community college for two years in a confusing, complicated admissions process.

Here's how it will work:

Those eligible students -- meaning those who completed the proper high school coursework and earned high enough grades and test scores -- who don't get into the campus of their choice will receive a rejection letter sometime this month indicating they will receive a second letter on or after April 15. This second "alternate admission letter" will offer one of two options:

• A chance to go to the campus they applied to after completing two years at a community college.

• A chance to go to UC Riverside or UC Merced, also after having completed two years at a community college. The state will likely waive the community college fees.

No longer will eligible students who are rejected at their first-choice UC campus be guaranteed a spot elsewhere in the system as a freshman (except for a very few freshmen engineering students who will be offered a spot at UC Riverside).

This is a big change for the UC system. The 1960 Master Plan for Higher Education guaranteed UC would accept the top 12.5 percent of high school graduates or all eligible students.

In years past, UC had the room and means to absorb every eligible student who wanted to attend. Last year, eligible students who didn't get their first choice were offered a chance to go to Riverside for their first year. In 2002, both the Riverside and Santa Cruz campuses had room. But as the college-age population boomed and budget cuts deepened, the campuses have become more selective.

UC Merced, the system's ninth undergraduate campus, is scheduled to open in fall 2005 for 900 undergraduates and add about 1,000 each year. So it should be ready by fall 2006 to accept the students who are sent this fall to a community college for two years.

"We see ourselves as a release valve in the higher education realm, making sure that students have a place where they can study if they are UC qualified," said UC Merced spokeswoman Patti Istas.

Riverside and Santa Cruz are mailing acceptances and rejections this week. The rest of the campuses, except Berkeley, will mail them in mid-March. Berkeley will notify applicants March 30. Some applicants will be able to check online.

One quasi-bright spot in all of this year's uncertainty: For the first time in a decade, applications to UC have dropped, fueling speculation that UC may not have to turn away as many students as it anticipated. UC received 4.1 percent fewer applications from prospective freshmen for fall 2004 than for last fall, the first decrease in applications since fall 1993.

Head counselor Larry Cebull at Miramonte High in Orinda said he doesn't think many students who have long planned on attending UC will want to spend two years at a community college.

"My feeling is the majority will go to a four-year university for the four-year experience."