Prince George's County officials have applied for a $99,263 grant from the Maryland Mass Transit Administration to serve older residents of the county. The proposal submitted by the county's Department of Public Works and Transportation calls for improvements to services in New Carrollton, Landover Hills and Seat Pleasant and for the Easter Seal Capital Assistance Transportation Program.

The county says it would like to provide 12-passenger vans for transporting older persons in New Carrollton and Landover Hills. The transport service would get administrative support from New Carrollton and the county's office of transportation. Suicide Prevention Hot Line to Open

The Prince George's County Mental Health Association is launching a suicide prevention phone service next Tuesday Christmas Eve, with a 24-hour telephone line and a year-round public education program.

The suicide program's telephone number is 731-0004. The number of the 24-hour "crisis hot line" is 577-4866. Human Relations Commission Honors 2 Groups

The Prince George's Human Relations Commission has honored two county organizations for the help they have given county residents.

The county chapter of the National Council of Negro Women was given the Theresa Banks Award for having raised money for the Hospital for Sick Children in the District, sponsored youths in the Maryland Special Olympics, and given Christmas gifts at the Boys Village in Cheltenham.

The county chapter of the Zeta Phi Beta Sorority -- which was founded 36 years ago by Theresa Banks, who also helped establish the commission -- received a community service award for its work at area mental health institutions and hospitals, with patients at the Washington Hospice Facility and for collecting clothes for the needy.