Starting Jan. 1, the monthly rate that an estimated 1,300 area senior citizens pay for medical coverage will nearly triple as a result of higher costs and limited federal reimbursement, officials of M.D.-Individual Practice Association said yesterday.

Rates also may increase -- though not as dramatically -- for an estimated 108,300 regular members of M.D.-IPA, a health maintenance organization formed in 1979 to serve residents of the Washington-Baltimore area, said Joseph L. Guarriello, vice president of corporate affairs.

The actual increase for regular members will vary widely, however, depending on the kind of coverage that person has and how much the person's employer contributes, Guarriello said.

Hardest hit of M.D.-IPA members will be the 1,300 persons aged 65 or older who belong to the special senior care program, which was launched five years ago and operated under contract with the U.S. Health Care Financing Administration, Guarriello said.

Members of the senior care program, who have been paying $22.22 a month each to M.D.-IPA, will be charged $62.13 a month under the new rate schedule, Guarriello said. At the same time, their benefits will shrink, Guarriello said. For example, M.D.-IPA no longer will reimburse for purchases of medications, he said.

Guarriello said that the cost of providing services for seniors has risen 20 percent this year. Yet, he said, Medicare has agreed to increase its contributions for 1988 by only about 12 percent over 1987.

The combination of those trends, he said, prompted the organization's need to raise rates and reduce benefits for next year.

Notices were mailed to seniors as soon as the changes were approved Dec. 1 by HCFA, Guarriello said.

And seniors reacted as soon as they received the news.

"They are saying they can't afford it," said Lynn Chaitovitz, a planner with the Montgomery County Division of Elder Affairs, which received a number of telephone calls from concerned seniors.

Chaitovitz said the county had been providing interested persons with a list of organizations that provide medical coverage, so that they could shop around for another provider. However, she said, many seniors probably would be unable to complete their shopping and change their coverage in time to avoid the Jan. 1 rate increase.

"Also, if they have a pre-existing medical condition, they may not be able to change," Chaitovitz said.