After four years of debate and opposition, the Maryland Senate approved today an agricultural land preservation bill designed to help state farmers resist pressures to sell their land to developers.

The bill, which has yet to be approved by the House, would authorize the state to buy from farmers their rights to develop their own land. After the state purchased the development rights, farmers would be forbidden from developing the land for at least 25 years before they could apply to purchase the rights back from the state.

If the bill is approved by the House and signed by the governor, the land preservation program will be ready for implementation - almost. At the moment, the Senate has made no provision for appropriating money to pay for development rights.

Sen. James Clark (D-Howard), the bills sponsor, has estimated the program would cost about $10 million next year, and rise to a maximum of $18 million by 1982. He has advanced several proposls for paying for the program, but each has been rejected at least once by the Senate Finance Committee, which Clark chairs.

'This bill either holds out to people in agriculture a false hope that there will be preservation in agriculture a false hope that there will be preservation in agriculture, or as sure as the night follows the day we'll have to (pass a new tax to) fund this bill," said Sen. John P. Corderman (D-Washington), who voted against the bill.

"Any number of people in this Senate has told me "I'm for the preservation bill, but there's no way I'm going to vote for" more taxes, said Corderman.

Clark originally proposed a tax on nonreturnable bottles to fund the program. With the vigorous opposition of organized labor, the bottle tax proposal was defeated.

Clark then resurrected an older idea, that of increasing the transfer tax, the tax paid at the time any land changes hands, by 50 per cent to three-quarters of 1 per cent of the value of the land.

The finance committee defeated the transfer tax proposal during the legislative off-season, but Clark has submitted nevertheless a bill that would increase the tax. If that bill is approved, said Sen. Victor L. Crawford (D-Montgomery), it would raise the total state and local transfer tax on an average Montgomery County home to more than $1,000.

Concern about the transfer tax was almost the only opposition voiced to the farmland preservation bill, as it passed the Senate by a vote of 40 to 6.

"I think this bill is a conservative approach to a very difficult problem," said Clark. According to Frank Bentz of the University of Maryland agricultural service, the number of farms in Maryland fell from 36,100 in 1949, when the state was overwhelmingly rural, to about 15,000 today, in the wake of two decades of rapid development.

About 64 per cent of Maryland's land was farmland in 1949, Bentz said, a figure that has fallen to about 40 per cent today. Neighboring Pennsylvania and Virginia both have more of their acreage in farmland than does Maryland, Bentz said.

Only land that is actively farmed is eligible for the program. Farmers interested in selling their development rights to the state would offer the rights for sale at a price somewhere in the range of the difference between the agricultural value of their land and the fair market value.

Thus a farmer whose land is assigned a fair market value of $2,000 an acre but is taxed at $1,000 because it is used agriculturally could offer to sell the development rights to his land for anywhere between $1 and $999 an acre, the difference between the two values.

The state would rank the offers in an order determined by the percentage of discount from fair market value bid by the farmers, then go down the list buying development rights until money for a given year is exhuasted.

Thus, a farmer who offered his development rights for sale at 50 per cent of the difference between his land's agricultural and fair market values would be placed higher on the list than a farmer who offered his rights for sale at 80 per cent of the difference between the two values for his land.

Any purchase of development rights would have to approved by a Maryland Agricultural Land Preservation Foundation created by the bill, as well as the county in which the land is located, and the state treasurer.

If a farmer sells his rights, he would be permitted to build only structures connected to the farm operation.

In other action, the Senate passed and sent to the House four major pieces of legislation.

One would raise the maximum weekly benefits for persons collecting unemployment insurance from $89 to $102, and impose an additional tax on businesses that lay off large numbers of workers to raise the $165 million to pay for the increase.

A second would require judges to sentence prisoners convicted of sexual attacks on fellow prisoners to consecutive rather than concurrent sentences, despite a warning from Sen. Robert L. Douglass (D-Baltimore), that the bill would "basically never be enforced" because it would be impossible to get witnesses to testify.

The third would alter the formula for calculating eligibility for Medicaid by including increases in Social Security payments that have not been computed since 1971. The bill would cost some 18,000 elderly persons an average of $30 a year in taxes, according to testimony.

The final bill would make it a misdemeanor, punishable by a fine of $10,000 or imprisonment for 10 years, or both, to lie to legislative committees in testimony.