Chesapeake & Potomac Telephone Co. yesterday announced it was seeking a 50 percent increase in telephone bills for most Virginia residents, in a move to shift more of the the costs of local service onto residential consumers rather than business.

The rate request comes just four months after the Virginia State Corporation Commission granted C&P a 6.4 percent across-the-board increase. The company said it needed an extra $134.8 million to cope with increased costs and competition largely as a result of the breakup of the American Telephone & Telegraph Co.

The request reflects the nationwide trend by AT&T subsidiaries to seek steep local rate increases, largely in preparation for the Bell System break-up. In 34 cases now pending before state commissions, Bell's local operating companies are seeking more than $9 billion in local rate increases. Already this year, more than $1 billion in local rate increases has been granted to Bell subsidiaries.

Also in keeping with the nationwide trend among Bell system telephone companies, C&P is seeking permission to implement the controversial local measured service in which customers would be charged on the length, distance and time of day of each phone call. The company is asking for state approval to offer the measured service as an option for customers who make a limited number of telephone calls each month.

C&P said yesterday rates would remain virtually the same for Northern Virginia businesses under the request filed before the state corporation commission. The effect of the proposed increase, however, would vary across the state. While Northern Virginian businesses would see almost no rate increases because they pay on a per-call basis, Richmond businesses, which now pay flat rates for telephone service, would pay almost 50 percent more in their bills, if the request is approved.

If C&P's rate request is approved, Northern Virginia residents would see the bulk of the increase in their residential bills in the monthly fee for unlimited service, which would rise to $18.77 from $12.55. About two-thirds of C&P residential customers use this service.

However, the increase would not be as steep for the one-third of C&P customers who now pay $8.78 a month for measured service, which allows 50 free calls, with each additional call costing 10.6 cents. This rate would increase to $9.72, but the 10.6 cents rate would same.

Rates would decline by 11 percent for the small percentage of C&P customers who have economy services 10.6 cents. This rate would decrease from $6.25 a month to $5.52.

Additionally, C&P proposes to:

Off monthly residential fees local measured service in which each call a customer makes would be billed like a long to the length of the call, the distance it travels over the telephone network and the time of day it takes dule will be determined if the commission approves this scheme.

* Raise the cost of pay-phone calls from 20uging that the cost of a pay-phone call has not changed in eight years.

* Increase the charge for calling d than six times a month from 10 cents for each additional call to 29 cents.

* Sharply hike installation cosidential customers would pay $87.35, compared to the current $49.99, while business customers would pay $112.4 of $81.82.

* Lower the cost of long-distance intrastate calls by 9.2 percent.

C&P officials say that thse steeper increases on residential users to reflect more accurately the costs of its service. Bell company ofed that the price of residential service has been kept below costs, because the service has been subsidized byistance operations, which have traditionally been priced above con in the long-distance business increasing, AT&T says it can no longer continue that practice. As a result, rs the nation are seeing higher rate increases.

In Maryland, C&P is asking for a $218 million increase that e Maryland residents pay for local service. Meanwhile, in the District, C&P is seeking to triple local phone blion rate increase.

It is unclear how successful C&P will be in its request in Virginia. Last year, the comntical request in terms of dollars, but the state commission granted just a little less than half the amount.