The United Steelworkers approved a new three-year contract emphasizing income security for senior workers yesterday after initially rejecting the agreement in a surprise rebuff to the union's leadership.

Although the contract was ultimately ratified by a 193-to-99 vote of local union presidents, the earlier 148-to-143 vote to reject it appeared to ensure continued dissension within the AFL-CIO's largest industrial union.

The contract, which does not have to be voted on by the rank and file, included a modest wage gain that union officials estimated would raise the existing average hourly wage of slightly more than $8 an hour by 10 to 15 per cent over the three-year life of the pact, not including cost-of-living increases and fringe benefits.

While the total cost of the package was not available, it did not appear that the settlement would exceed economists' predictions of moderate pay increases for 1977, with little resulting impact on the rate of inflationary growth.

But the contact broke new ground in providing a varied package of job security benefits aimed especially at workers with 20 years or more on the job, including optional earlier retirement, an extra pension benefit for those who retire early because of layoffs or disability and extended supplemental unemployment benefits and disability coverage.

It also continued the steel industry's experimental no-strike agreement, which probably would have been junked if the initial negative vote had prevailed and the contract had gone to arbitration.

Under the voluntary no-strike pact, which was adopted in 1973 and is unique among major unions, unresolved issues are submitted to an arbitration panel in order to avoid work stop-pages and the boom-bust cycle of production, stockpiling and work layoffs that marked the industry prior to the agreement's adoption.

Consequently a strike was never a possibility this year even though negotiators failed to meet their self-imposed deadline of Thursday night for an agreement and the contract was almost rejected.

The brief revolt, reflecting lingering hostilities from the union's leadership fight earlier this year, was an embarrassment to retiring USW President I. W. Abel, who wanted the contract - with its start toward his goal of lifetime job security - as the capstone of his 40-year career with the union.

It was also the harbinger of future problems for President-elect Lloyd McBride, who, with Abel's backing, defeated Ed Sadlowski, a militant union dissident, in a bitter fight last February for presidency of the 1.4 million-member union.

McBride, who recommend adopton of the contract as a "good settlement, said the initial votes against it came largely from the Sadlowski bloc. He said it was basically an "emotional" vote and noted that many presumably pro-ratification union officials had left town earlier, assuming the contract was safe.

But one dissident, Anthony Tomko, president of USW Local 1406 in McKeesport, Pa., said the problems ran deeper. "They're not going to ignore the rank and file anymore," he told reporters outside the closed-door ratification session at the Shoreham Americana Hotel here. "It's actually a vote of no confidence. They lost their prestige."

McBride, who left the session before the vote was complete to return home to St. Louis, said he believed the contract provided a "good start" toward lifetime job security in the steel industry, adding, "You can only do so much at one time."

His contention was echoed by Abel later at a joint press conference with industry representatives. But it was clear that there was still a long way to go before meeting Abel's goal, proclaimed at the start of negotiations, of "a job for life with a decent, respectable income for life," as a matter of basic right.

Neither Abel nor J. Bruce Johnston, vice chairman of the U.S. Steel Corp. and the industry's chief negotiator, said they could estimate the overall cost of the settlement. Nor, they said, could they pinpoint the value of individual workers' gans.

But Johnston said he believed the package was comparable to last year's auto workers' settlement, which amounted to an overall increase of 34 per cent over three years.

Abel denied that the agreement would be inflationary, but Johnston indicated it might lead to higher steel prices, saying, "We all know that ultimately prices must cover costs."

The contract, which takes effect Aug. 1, covers 340,000 workers in the nation's 10 largest steel companies and is expected to become the pattern for settlements covering 180,000 workers in other steel plants. It also is considered likely to have an impact on other negotiations this year, including other metals, communications, coal and railroads.

The contract provides for flat-rate wage increases of 80 per cents an hour over three years in increments of 40,20 and 20 cents. Incentive pay for extra work will add at least an additional 10 cents, a union lawyer estimated. Previously won cost-of-living protections will add more as costs rise.

Pension and supplemental jobless benefits, which are provided on top of regular unemployment insurance, also will be increased.

Earlier retirement was sanctioned by permitting workers to retire after age and years of service add up to 65, so long as they've worked 20 years. And a $300 monthly supplement will be offered to these early retirees - if they have been forced out by disability extended job layoffs - until they become eligible for Social Security.

Industry will increase its contribution to supplemental unemployment benefits by 20 per cent. This will raise payments from $100 to $125 a week for workers still eligible for government payments and from $135 to $170 for those who aren't. Such payments are now made for one year and will be extended to two years for workers with 20 years or more seniority.

Also provided were increased life-insurance coverage, eye care in addition to medical and dental coverage and limited protection against contracting out work that could be done by steelworkers while a joint labor-management commission studies the overall problem of giving work to non-employees.

While no industrywide strike can be held, local's strikes will be permitted after the current contract expires July 31. Johnston said he did not expect "a rash of local strikes" because the negotiators made progress on settling local issues. Abel noted that there were no local strikes three years ago.