AUGUSTA — A bill to limit paper-mill discharges that create color, odor and foam in Maine’s rivers was enacted and sent to the governor Friday night after the House and Senate struck a compromise that will ease the impact on a mill on the Penobscot River.

The Senate, which a day earlier had favored the less stringent of two competing proposals, agreed to the amended version of the more stringent plan by a vote of 16-13. Soon afterward, the House gave its final approval to the proposal 87-37. The Senate followed suit without a head count.

The amended bill would require kraft-process mills to limit discharges to 225 pounds of color per ton of pulp manufactured, the same standard contained in the proposal previously approved by the House. The amendment was intended to clarify an exemption that some observers said already would have been provided to the James River Corp. mill in Old Town, whose discharges are diluted more quickly than mills along smaller, slower-moving rivers.

An aide said Gov. John R. McKernan would sign the bill, even though the amendment sets a single standard for the amount of color change in Class B and C rivers, rather than setting a stricter standard for Class B waters. The James River mill is located on a Class B stretch of water.

“It’s not as good” as the House-backed version, “but it’s acceptable,” said Alan MacEwan.

Some Democrats maintained that the compromise bill was essentially similar to legislation that McKernan vetoed last year on grounds that not enough study had been done. MacEwan said the vetoed bill would have resulted in unacceptably low limits for certain mills.

Friday’s voting was accompanied by sharp legislative criticism of a full-page newspaper ad attacking two lawmakers for their advocacy of the proposal that the House had backed Thursday.

The outcry generated by the S.D. Warren Co. ad also appeared to play a part in dooming a major state land acquisition.

The company’s “open letter” was addressed to Sen. Judy C. Kany, the Waterville Democrat who co-chairs the Energy and Natural Resources panel, and Rep. Paul F. Jacques, an outspoken Democrat also from Waterville. It said the tougher proposal would force S.D. Warren, a subsidiary of Scott Paper Co., to spend between $70 million and $170 million on plant modifications.

“Your committee vote is a clear signal to my company that you don’t care whether we remain competitive or not,” Allan N. Robinson, manager of the S.D. Warren mill in Skowhegan, wrote in the letter, which was published in Friday’s editions of the Kennebec Journal in Augusta.

“It is a huge amount of money. In fact, this would be, by far, the largest single expenditure ever imposed upon any Scott mill, any place in the country by state legislation.

“Ironically, everyone, including the Department of Environmental Protection, agrees that health is not the issue. Apparently, you have chosen to disregard these facts,” Robinson wrote.

The ad provoked widespread legislative displeasure ranging across party lines. Democratic and Republican Senate leaders rose in succession during floor debate to denounce what Majority Leader Nancy Randall Clark called “a shameful personal attack” on Kany and Jacques.

Clark, D-Freeport, urged that the sponsor of the ad be “condemned” by other paper companies, saying, “I think it’s important that Scott Paper Co. be disciplined by the industry it serves.”

In a bipartisan closing of ranks, Republican Senate leader Charles M. Webster joined in castigating the company and told Democrats the ad was “not something that we were a part of or would agree with.”

Similar sentiments were expressed in the House, where Rep. Patrick K. McGowan, D-Canaan, read the ad aloud in its entirety.

At the same time, a bipartisan Senate majority voted to reject a proposed land trade between the state and S.D. Warren designed to give the state nearly 20 miles of lake frontage on Moosehead Lake and Bald Mountain Pond. In return, S.D. Warren was to receive more than 19,000 acres of forest land.

MacEwan called the Senate rejection “a very unfortunate loss to the people of the state of Maine.”

Asked if the negative vote could be attributed to a backlash against the paper company ad, MacEwan said, “It didn’t help.”

Echoed Assistant Senate Majority Leader Dennis L. Dutremble, D-Biddeford, “that’s exactly right.”

Dutremble said he believed Senate members based their votes on “the merits of the issue.”